Something appears to mess with PATH on Travis Linux when running tests

I pushed a repo to Travis that is just the TypeScript extension sample with a travis file that echos the PATH in the Travis script, the npm test script and then also inside the sample test. The values are different. Significantly, the path to node has been removed by the time we get into the tests. In my real project, this means my tests are failing because they use the DebugClient and pass node as the executable.

Here's the code:
https://github.com/DanTup/vscode_extension_path_test

Here's the Travis log:
https://travis-ci.org/DanTup/vscode_extension_path_test/jobs/362281254

Here's the relevant parts:

PATH as output in the travis file:

./node_modules/.bin:/home/travis/bin:/home/travis/.local/bin:/opt/pyenv/shims:/home/travis/.phpenv/shims:/home/travis/perl5/perlbrew/bin:/home/travis/.nvm/versions/node/v8.11.1/bin:/home/travis/.kiex/elixirs/elixir-1.4.5/bin:/home/travis/.kiex/bin:/home/travis/.rvm/gems/ruby-2.4.1/bin:/home/travis/.rvm/gems/ruby-2.4.1@global/bin:/home/travis/.rvm/rubies/ruby-2.4.1/bin:/home/travis/gopath/bin:/usr/local/phantomjs/bin:/usr/local/phantomjs:/usr/local/neo4j-3.2.7/bin:/usr/local/maven-3.5.2/bin:/usr/local/cmake-3.9.2/bin:/usr/local/clang-5.0.0/bin:/home/travis/.gimme/versions/go1.7.4.linux.amd64/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/home/travis/.rvm/bin:/home/travis/.phpenv/bin:/opt/pyenv/bin:/home/travis/.yarn/bin

PATH as output by prefixing the test script in package.json with echo $PATH:

/home/travis/.nvm/versions/node/v8.11.1/lib/node_modules/npm/node_modules/npm-lifecycle/node-gyp-bin:/home/travis/build/DanTup/vscode_extension_path_test/node_modules/.bin:./node_modules/.bin:/home/travis/bin:/home/travis/.local/bin:/opt/pyenv/shims:/home/travis/.phpenv/shims:/home/travis/perl5/perlbrew/bin:/home/travis/.nvm/versions/node/v8.11.1/bin:/home/travis/.kiex/elixirs/elixir-1.4.5/bin:/home/travis/.kiex/bin:/home/travis/.rvm/gems/ruby-2.4.1/bin:/home/travis/.rvm/gems/ruby-2.4.1@global/bin:/home/travis/.rvm/rubies/ruby-2.4.1/bin:/home/travis/gopath/bin:/usr/local/phantomjs/bin:/usr/local/phantomjs:/usr/local/neo4j-3.2.7/bin:/usr/local/maven-3.5.2/bin:/usr/local/cmake-3.9.2/bin:/usr/local/clang-5.0.0/bin:/home/travis/.gimme/versions/go1.7.4.linux.amd64/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/home/travis/.rvm/bin:/home/travis/.phpenv/bin:/opt/pyenv/bin:/home/travis/.yarn/bin

PATH as output in tests:

/home/travis/.local/bin:/opt/pyenv/shims:/home/travis/.phpenv/shims:/home/travis/perl5/perlbrew/bin:/home/travis/.kiex/elixirs/elixir-1.4.5/bin:/home/travis/.kiex/bin:/home/travis/.phpenv/shims:/home/travis/gopath/bin:/home/travis/.gimme/versions/go1.7.4.linux.amd64/bin:/usr/local/phantomjs/bin:/usr/local/phantomjs:/usr/local/neo4j-3.2.7/bin:/usr/local/maven-3.5.2/bin:/usr/local/cmake-3.9.2/bin:/usr/local/clang-5.0.0/bin:/home/travis/.gimme/versions/go1.7.4.linux.amd64/bin:/usr/local/phantomjs/bin:/usr/local/phantomjs:/usr/local/neo4j-3.2.7/bin:/usr/local/maven-3.5.2/bin:/usr/local/cmake-3.9.2/bin:/usr/local/clang-5.0.0/bin:/home/travis/.nvm/versions/node/v8.11.1/lib/node_modules/npm/node_modules/npm-lifecycle/node-gyp-bin:/home/travis/build/DanTup/vscode_extension_path_test/node_modules/.bin:./node_modules/.bin:/home/travis/bin:/home/travis/.local/bin:/opt/pyenv/shims:/home/travis/.phpenv/shims:/home/travis/.kiex/elixirs/elixir-1.4.5/bin:/home/travis/.kiex/bin:/home/travis/.rvm/gems/ruby-2.4.1/bin:/home/travis/.rvm/gems/ruby-2.4.1@global/bin:/home/travis/.rvm/rubies/ruby-2.4.1/bin:/home/travis/gopath/bin:/usr/local/phantomjs/bin:/usr/local/phantomjs:/usr/local/neo4j-3.2.7/bin:/usr/local/maven-3.5.2/bin:/usr/local/cmake-3.9.2/bin:/usr/local/clang-5.0.0/bin:/home/travis/.gimme/versions/go1.7.4.linux.amd64/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/home/travis/.rvm/bin:/home/travis/.phpenv/bin:/opt/pyenv/bin:/home/travis/.yarn/bin:/home/travis/.phpenv/bin:/opt/pyenv/bin

Note that /home/travis/.nvm/versions/node/v8.11.1/bin exists in the first and second, but not the last one (the one from inside the tests).

Start with the Travis configuration and the package.json test script in the linked sample repository, then compare the PATH values printed there with the value printed by the sample test. Trace where the PATH changes before the test runs; done means the test retains the Node executable path and the reported DebugClient scenario passes.