Remove test/bower_components from gitignore list

No need to specify test/bower_components in gitignore, if bower_components folder was added without slash `"/"`. From git docs:
> If the pattern does not contain a slash '/', Git treats it as a shell glob pattern and checks for a match against the pathname relative to the location of the .gitignore file (relative to the toplevel of the work tree if not from a .gitignore file).