Remove ./node_modules/.bin from $PATH

[BanzaiMan]

Some npm modules define commands with widely used bash functions
(and probably others).
Putting this component in $PATH causes subtle issues, such as
travis-ci/travis-ci#5092.
We are removing it, so that this is no longer the case.

This will most likely break some builds, so we add a warning.

[BanzaiMan]

Tested in staging.

Before: https://staging.travis-ci.org/BanzaiMan/travis_staging_test/builds/528065#L168
After: https://staging.travis-ci.org/BanzaiMan/travis_staging_test/builds/528067#L160-L178

[nathanhammond]

Note that, to my knowledge, this change breaks every Ember addon out there because of our default blueprint: https://github.com/ember-cli/ember-cli/blob/74562a4/blueprints/addon/files/.travis.yml#L40

[backspace]

This will break things for almost all Ember projects, as ember test is the default way to run tests and that assumes the Node-installed ember command is available.

[nathanhammond]

This doesn't appear to have landed yet we currently have reported failures from users in our Slack channel. Also, hi, @backspace! <3

[joshk]

I'm not sure I support this change. This will cause major issues for many people using Node.

[Turbo87]

@BanzaiMan instead of removing the path completely, would it maybe be possible to move it to the end of the list as a fallback? that way the native executables are preferred, but the Ember addon builds won't fail.

[BanzaiMan]

The offending bit is travis-ci/travis-cookbooks#786, which renders this PR obsolete. I'll work on a fix for the issue shortly.

[kevinji]

Since this PR is now obsolete, it can be closed now right?