updating activation mail, adding Gemfile.lock to gitignore

.gitignore

@@ -21,3 +21,4 @@ reports/
 /src/
 \#*\#
 *.egg-info
+Gemfile.lock

lms/templates/emails/activation_email.txt

@@ -6,7 +6,7 @@ this address into your web browser's address bar:
 % if is_secure:
   https://${ site }/activate/${ key }
 % else:
-  http://edx4edx.mitx.mit.edu/activate/${ key }
+  http://${ site }/activate/${ key }
 % endif
 
 If you didn't request this, you don't need to do anything; you won't