docs(error/ng/btstrpd): fix typo in error page

Minimal typo fix

Closes #6803
docs(guide/directive): fix broken link

Fix broken internal link in directive documentation.

Closes #6802
docs(faq): fix link to Closure Library

The previous link throws a 404.
fix(doc-gen): Run Gulp on Windows too

Using node_module/.bin/gulp will enable to gulp command to run
both on Windows and Linux. In its current form, the default action of
executing a Javascript file on Windows does not use node.
Requires quotes around the command to correctly resolve path on Windows

Closes #6346
chore(docs): remove px declaration from x,y coordinates in header svg