[ci] Install 'which' in ArchLinux bot
diff --git a/.circleci/config.yml b/.circleci/config.yml
index 4fb05c3..e18cf60 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -63,7 +63,7 @@
       - image: archlinux/base
     steps:
       - checkout
-      - run: pacman --noconfirm -Syu freetype2 cairo icu gettext gobject-introspection gcc gcc-libs glib2 graphite pkg-config ragel python python-pip make
+      - run: pacman --noconfirm -Syu freetype2 cairo icu gettext gobject-introspection gcc gcc-libs glib2 graphite pkg-config ragel python python-pip make which
       - run: pip install flake8 fonttools
       - run: flake8 . --count --select=E901,E999,F821,F822,F823 --show-source --statistics
       # C??FLAGS are not needed for a regular build