Remove node_modules cache from .travis.yml

[jdonaghue]

Type: bug

Description:

Remove node_modules cache from .travis.yml

Related Issue: https://github.com/dojo/dojo2-package-template/issues/75

Please review this checklist before submitting your PR:

• [x] There is a related issue
• [x] All contributors have signed a CLA
• [x] All code matches the style guide
• [x] The code passes the CI tests
• [x] Unit or Functional tests are included in the PR
• [x] The PR increases or maintains the overall unit test coverage percentage
• [x] The code is ready to be merged

[codecov-io]

Current coverage is 99.09% (diff: 100%)

Merging #82 into master will not change coverage

@@             master        #82   diff @@
==========================================
  Files            10         10          
  Lines           222        222          
  Methods           0          0          
  Messages          0          0          
  Branches         19         19          
==========================================
  Hits            220        220          
  Misses            0          0          
  Partials          2          2          

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