fix(jenkins): reset baseUrl in protractor conf

(Tested before and after fix locally and manually on ci.angularjs.org)

Commit 22b817ec11f7ab1a81342a4b60acd644a3f2a8c3 changed the url
used by protracts in all docs tests to add build/docs, which
was already set to the baseUrl in protractor-jenkins.conf. This
commit just changes the protractor config's baseUrl to adapt
to the changes in the spec files.

Closes #9783