Fix install-chruby.sh and ruby-install.sh

Currently, these scripts leave behind cruft in the home directory, since
the `rm` command is actually called from within the src directory. This
patch is in line with the original intent of the code, to cd back into
the home directory and remove src tarball and folder.
Merge pull request #1 from jrhorn424/fix-chruby-rubyinstall

Fix install-chruby.sh and ruby-install.sh

Currently, these scripts leave behind cruft in the home directory, since
the rm command is actually called from within the src directory. This
patch is in line with the original intent of the code, to cd back into
the home directory and remove src tarball and folder.