Better `cd` in installer

With `cd "$(dirname $)"/..` it works bad, because `$(dirname $)` will return `.` so it implies that to correctly works, you have to be in the `script` directory, otherwise if you're e.g. in `$HOME/.dotfiles` you'll go in `$HOME` and then look for all `install.sh`, which may not be what you intended to do.

Using `$(dirname $0)` instead ensure that you'll go one level higher than the `install` script.
Merge pull request #127 from chadrien/patch-1

Better `cd` in installer
Only source grc if grc and brew are installed
Merge pull request #128 from jacobwg/fix-grc

Only source grc if grc and brew are installed
Misspeled git rank-contributors alias
Merge pull request #129 from kibao/hotfix/git-rank-contributors-misspelled

Misspeled git rank-contributors alias
Fixed git status parsing for git 1.8.5
Merge pull request #130 from pmcdaniel/fixGitStatusParsing

Fix "git status" parsing in prompt for git 1.8.5
Revert "Merge pull request #130 from pmcdaniel/fixGitStatusParsing"

This reverts commit cfd5d1bcd0cd93871ce174be4c709304f3bce28d, reversing
changes made to e28115a83335cbac70098f884d587973458782de.
Fix `res` for Mavericks (closes #116)
Merge remote-tracking branch 'upstream/master'