fix(jenkins): Fix the format for passing parameters to Grunt tasks

The Jenkins build.sh script has to be updated as the previous way of
specifying parameters to the code run in Grunt tasks stopped working
with the newest Grunt. This has been previously fixed for the Travis
build.sh but wasn't done for the Jenkins one.

Also, the contribute docs were updated to account for the new format.

docs/content/misc/contribute.ngdoc

@@ -139,7 +139,7 @@ grunt test:unit
 To run the tests on other browsers (Chrome, ChromeCanary, Firefox, Opera and Safari are pre-configured) use:
 
 ```shell
-grunt test:unit --browsers Opera,Firefox
+grunt test:unit --browsers=Opera,Firefox
 ```
 
 Note there should be _no spaces between browsers_. `Opera, Firefox` is INVALID.

scripts/jenkins/build.sh

@@ -28,13 +28,13 @@ grunt ci-checks package --no-color
 mkdir -p test_out
 
 # UNIT TESTS #
-grunt test:unit --browsers $BROWSERS --reporters=dots,junit --no-colors --no-color
+grunt test:unit --browsers="$BROWSERS" --reporters=dots,junit --no-colors --no-color
 
 # END TO END TESTS #
 grunt test:ci-protractor
 
 # DOCS APP TESTS #
-grunt test:docs --browsers $BROWSERS --reporters=dots,junit --no-colors --no-color
+grunt test:docs --browsers="$BROWSERS" --reporters=dots,junit --no-colors --no-color
 
 # Promises/A+ TESTS #
 grunt test:promises-aplus --no-color