Slashify Ruby files and directories.

Perhaps this is a little pedantic, but without the initial / all
such matches within the repository get ignored, and without the
trailing slash files as well as directories of that name get ignored.
e.g. Specifying `tmp` and `test/tmp` without slashes is redundant, as
`tmp` already ignores `test/tmp`, as well as every other `tmp` and
`tmp/`.

Ruby.gitignore

-*.gem
-*.rbc
-.config
-coverage
-InstalledFiles
+/*.gem
+/*.rbc
+/.config
+/coverage/
+/InstalledFiles
 /pkg/
-/spec/reports
-/test/tmp
-/test/version_tmp
+/spec/reports/
+/test/tmp/
+/test/version_tmp/
 /tmp/
 
 ## Documentation cache and generated files:
-/.yardoc
-/_yardoc
+/.yardoc/
+/_yardoc/
 /doc/
-/rdoc
+/rdoc/
 
 ## Environment normalisation:
-/.bundle
-/lib/bundler/man
+/.bundle/
+/lib/bundler/man/
 
 # for a library or gem, you might want to ignore these files since the code is
 # intended to run in multiple environments; otherwise, check them in:
@@ -26,4 +26,4 @@ InstalledFiles
 # .ruby-gemset
 
 # unless supporting rvm < 1.11.0 or doing something fancy, ignore this:
-.rvmrc
+/.rvmrc