add alecjacobson (devel) branch to appveyor

Former-commit-id: 0f48960794c1fa5b4d1790f61f70bdacb2d1ca22

.appveyor.yml

@@ -5,6 +5,7 @@ clone_folder: C:\projects\libigl
 branches:
   only:
     - master
+    - alecjacobson
 install:
   - git submodule update --init --recursive
   - cinstall: python