Update gitignore for compatibility with Coq master
See https://github.com/coq/coq/pull/10947 (.coqdeps.d now uses the name of the Coq Makefile) and https://github.com/coq/coq/pull/8642 (Coq now generates empty interface files *.vos when compiling).
See https://github.com/coq/coq/pull/10947 (.coqdeps.d now uses the name of the Coq Makefile) and https://github.com/coq/coq/pull/8642 (Coq now generates empty interface files *.vos when compiling).