.bash_profile: Redirect all which brew output

On RHEL6, `which brew` prints `/usr/bin/which: no brew in …` to stderr. Changing `> /dev/null` to `&>/dev/null` redirects both stdout and stderr to `/dev/null`, silencing the check completely.

Closes mathiasbynens#650.

.bash_profile

@@ -26,7 +26,7 @@ for option in autocd globstar; do
 done;
 
 # Add tab completion for many Bash commands
-if which brew > /dev/null && [ -f "$(brew --prefix)/share/bash-completion/bash_completion" ]; then
+if which brew &> /dev/null && [ -f "$(brew --prefix)/share/bash-completion/bash_completion" ]; then
 	source "$(brew --prefix)/share/bash-completion/bash_completion";
 elif [ -f /etc/bash_completion ]; then
 	source /etc/bash_completion;