Correct redirection of output from 'hash'

The intention of the redirection to /dev/null is to hide the output
'hash: no such command: git' since we rely on the exit status.

However, the output goes to stderr, so it's stderr that needs to be
redirected. For completeness, we redirect both stderr and stdout using
'2>&1'.

Example:

  [~]$ hash git > /dev/null
  [~]$ PATH=''
  [~]$ hash git > /dev/null
  hash: no such command: git
  [~]$ hash git > /dev/null 2>&1
  [~]$

tools/install.sh

@@ -10,7 +10,7 @@ if [ -d "$ZSH" ]; then
 fi
 
 echo "\033[0;34mCloning Oh My Zsh...\033[0m"
-hash git >/dev/null && /usr/bin/env git clone https://github.com/robbyrussell/oh-my-zsh.git $ZSH || {
+hash git >/dev/null 2>&1 && /usr/bin/env git clone https://github.com/robbyrussell/oh-my-zsh.git $ZSH || {
   echo "git not installed"
   exit
 }