Non default JAVA_HOME makes wrapper fail

If `java` is not on a default path (as set by /etc/default/login or other means), the wrapper fails since the executable cannot be found when doctoolchain is finally called.

The reason for this is the call to `bash` with the `-l` flag in line 37:
https://github.com/docToolchain/doctoolchain.github.io/blob/068e50e045af2e20cb230b5a08c24fc72e3bd93a/dtcw#L237

This causes bash to work as login shell and reset any environment variables to their login defaults.