suppress pip-grep errors

bin/steps/cryptography

@@ -20,7 +20,7 @@ source $BIN_DIR/utils
 bpwatch start libffi_install
 
 # If pylibmc exists within requirements, use vendored cryptography.
-if (pip-grep -s requirements.txt cffi pylibmc) then
+if (pip-grep -s requirements.txt cffi pylibmc &> /dev/null) then
 
   if [ -d ".heroku/vendor/lib/libffi-3.1.1" ]; then
     export LIBFFI=$(pwd)/vendor

bin/steps/pylibmc

@@ -19,7 +19,7 @@ source $BIN_DIR/utils
 bpwatch start pylibmc_install
 
 # If pylibmc exists within requirements, use vendored libmemcached.
-if (pip-grep -s requirements.txt pylibmc) then
+if (pip-grep -s requirements.txt pylibmc &> /dev/null) then
 
   if [ -d ".heroku/vendor/lib/sasl2" ]; then
     export LIBMEMCACHED=$(pwd)/vendor