Hide pub get output when updating flutter tool

Fixes https://github.com/flutter/flutter.github.io/issues/100

bin/flutter

@@ -17,7 +17,7 @@ DART=dart
 REVISION=`(cd "$FLUTTER_ROOT"; git rev-parse HEAD)`
 if [ ! -f "$SNAPSHOT_PATH" ] || [ ! -f "$STAMP_PATH" ] || [ `cat "$STAMP_PATH"` != "$REVISION" ] || [ "$FLUTTER_TOOLS_DIR/pubspec.yaml" -nt "$FLUTTER_TOOLS_DIR/pubspec.lock" ]; then
   echo Updating flutter tool...
-  (cd "$FLUTTER_TOOLS_DIR"; pub get)
+  (cd "$FLUTTER_TOOLS_DIR"; pub get > /dev/null)
   $DART --snapshot="$SNAPSHOT_PATH" --package-root="$FLUTTER_TOOLS_DIR/packages" "$SCRIPT_PATH"
   echo -n $REVISION > "$STAMP_PATH"
 fi