Remove extraneous newlines in pre-receive hook

Found while investigating slow performance in gitlab-org/gitlab-ce#17225

We were adding a newline for every branch push because:

1. GitlabAccess calls changes.lines, which keeps the newline (e.g. ['00000000 12345678 refs/heads/master\n'])
2. GitlabNet calls changes.join("\n"), which adds another newline

CHANGELOG

 v3.0.0
+  - Remove extraneous newlines in pre-receive hook
   - Remove rm-tag command (Robert Schilling)
   - Remove create-branch and rm-branch commands (Robert Schilling)
   - Update PostReceive worker so it logs a unique JID in Sidekiq

lib/gitlab_access.rb

@@ -16,7 +16,7 @@ class GitlabAccess
     @repo_path = repo_path.strip
     @actor = actor
     @repo_name = extract_repo_name(@repo_path.dup, config.repos_path.to_s)
-    @changes = changes.lines
+    @changes = changes.split("\n")
   end
   def exec

spec/gitlab_access_spec.rb

@@ -11,7 +11,7 @@ describe GitlabAccess do
     end
   end
   subject do
-    GitlabAccess.new(repo_path, 'key-123', 'wow').tap do |access|
+    GitlabAccess.new(repo_path, 'key-123', "first\nsecond\n").tap do |access|
       access.stub(exec_cmd: :exec_called)
       access.stub(api: api)
     end
@@ -24,7 +24,7 @@ describe GitlabAccess do
   describe :initialize do
     it { subject.repo_name.should == repo_name }
     it { subject.repo_path.should == repo_path }
-    it { subject.changes.should == ['wow'] }
+    it { subject.changes.should == ['first', 'second'] }
   end
   describe "#exec" do