Quote all strings to allow for whitespace.

This is not strictly necessary for all of the strings, but it is generally a
good practice in Bash. In particular, $GOPATH could contain spaces.
Merge branch 'quote-strings' of github.com:juliusv/johnny-deps

Conflicts:
	bin/johnny_deps
pointless checking
exit from main body not function
use PE instead of... that
also fail when vars are unset (eg. $GOPATH)
we already have set -e
Merge pull request #13 from git2samus/master

receive my h̶a̶t̶e̶ love!
Ignore empty lines
Merge pull request #15 from VividCortex/issues/14

Ignore empty lines
Update README.md
Update README.md
Handling path separators in GOPATH
Merge pull request #12 from meatballhat/gopath-is-not-singular

Handling path separators in GOPATH