build: don't install github templates

Avoid putting github templates in the source tarballs.

PR-URL: #5612
Reviewed-By: Rod Vagg <rod@vagg.org>
Reviewed-By: Rich Trott <rtrott@gmail.com>

Makefile

@@ -370,6 +370,7 @@ $(TARBALL): release-only $(NODE_EXE) doc
 	rm -rf $(TARNAME)/deps/uv/{docs,samples,test}
 	rm -rf $(TARNAME)/deps/openssl/{doc,demos,test}
 	rm -rf $(TARNAME)/deps/zlib/contrib # too big, unused
+	rm -rf $(TARNAME)/.github # github issue templates
 	find $(TARNAME)/ -type l | xargs rm # annoying on windows
 	tar -cf $(TARNAME).tar $(TARNAME)
 	rm -rf $(TARNAME)