Switch from /bin/sh to /bin/bash

You have bashisms in your script and /bin/sh might not always be bash. In that case the script would fail (for example on Ubuntu).
Remove unneeded shebang in nvm.sh
Overwritting GREP_OPTIONS on local script

(recommiting to automerge into current master)
Merge pull request #310 from danieltdt/grep-options

Overwritting GREP_OPTIONS on local script
Merge pull request #270 from hachre/patch-1

Switch from /bin/sh to /bin/bash
Unset the executable bit on nvm.sh, since it's meant to be sourced
Adding a CONTRIBUTING.md file
nvm exec wrapper to execute commands with a specific node version
Use has util method and use comparison opts
Merge pull request #372 from koenpunt/patch-1

Use has util method and use comparison opts
Merge pull request #319 from koenpunt/nvm-exec

nvm exec wrapper to execute commands with a specific node version
Files should end in trailing newlines
fixed nvm_version result when multiple versions match the given pattern
added test for using the latest of two versions
Merge pull request #366 from messju/nvm_version_fix

fixed nvm_version result when multiple versions match the given pattern
Replaced echo for printf when using formatted strings
Updated version list, now also compatible with zsh
updated tests for altered output
Added travis config, fixed tests for use on travis
Merge pull request #378 from koenpunt/ci

Added travis config, fixed tests for use on travis
Merge pull request #377 from koenpunt/remove-obscure-echo-test

Replaced echo for printf when using formatted strings