Stop testing against PhantomJS

PhantomJS is at end of life, and the last version of Selenium that supported
it was 3.6.0, released almost three years ago. We can't test Jasmine against
PhantomJS without pinning key pieces of the project to increasingly outdated
versions of key libraries.

.travis.yml

@@ -18,7 +18,6 @@ env:
 
 matrix:
   include:
-    - env: JASMINE_BROWSER="phantomjs" USE_SAUCE=false
     - env: JASMINE_BROWSER="firefox" SAUCE_BROWSER_VERSION='' SAUCE_OS="Linux"
       if: type != pull_request
       addons: