grpc_tools_node_protoc error messages are inscrutable

### Problem description
The `grpc_tools_node_protoc` error messages are inscrutable.

### Reproduction steps
I tried compiling some protos the other day following the instructions from https://github.com/grpc/grpc/tree/master/examples/node/static_codegen. Not only does it not works, but the error messages are just word soup:
```
nodejs_static [master ?] -> node_modules/.bin/grpc_tools_node_protoc --js_out=import_style=commonjs,binary:. --grpc_out=. --plugin=protoc-gen-grpc=`node_modules/.bin/grpc_tools_node_protoc_plugin` ../protos/pingpong.proto
/Users/samuelainsworth/Development/grpc-polyglot/nodejs_static/node_modules/grpc-tools/bin/protoc_plugin.js:37
throw error;
^

Error: spawn /Users/samuelainsworth/Development/grpc-polyglot/nodejs_static/node_modules/grpc-tools/bin/grpc_node_plugin ENOENT
at Process.ChildProcess._handle.onexit (internal/child_process.js:232:19)
at onErrorNT (internal/child_process.js:407:16)
at process._tickCallback (internal/process/next_tick.js:63:19)
at Function.Module.runMain (internal/modules/cjs/loader.js:745:11)
at startup (internal/bootstrap/node.js:279:19)
at bootstrapNodeJSCore (internal/bootstrap/node.js:752:3)
/Users/samuelainsworth/Development/grpc-polyglot/nodejs_static/node_modules/grpc-tools/bin/protoc.js:41
throw error;
^

Error: spawn /Users/samuelainsworth/Development/grpc-polyglot/nodejs_static/node_modules/grpc-tools/bin/protoc ENOENT
at Process.ChildProcess._handle.onexit (internal/child_process.js:232:19)
at onErrorNT (internal/child_process.js:407:16)
at process._tickCallback (internal/process/next_tick.js:63:19)
at Function.Module.runMain (internal/modules/cjs/loader.js:745:11)
at startup (internal/bootstrap/node.js:279:19)
at bootstrapNodeJSCore (internal/bootstrap/node.js:752:3)
nodejs_static [master ?] ->
```
If anyone happens to know why this doesn't work, please do let me know. But I'm really here to report that these error messages are very unhelpful.

### Environment
- OS name, version and architecture: macOS 10.13.6
- Node version: v10.11.0
- Node installation method: homebrew
- Package name and version: grpc-tools@1.6.6

### Additional context
Repo is here: https://github.com/samuela/grpc-polyglot.