re-add .bashrc to .gitignore

.bashrc was removed in 29fbc9cc1d67759974ec4cb746840ae160d842bc
but is still needed. It serves as a hook to customize the build environment.

Signed-off-by: Harald Albers <github@albersweb.de>

.gitignore

@@ -7,6 +7,8 @@
 *.test
 .*.swp
 .DS_Store
+# a .bashrc may be added to customize the build environment
+.bashrc
 .gopath/
 autogen/
 bundles/