BUILD: travis: remove the "allow_failures" entry

Now that OSX passes all regtests as well, remove this temporary entry.
diff --git a/.travis.yml b/.travis.yml
index 5042860..f689fe9 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -21,8 +21,6 @@
   - os: osx
     compiler: clang
     env: TARGET=generic FLAGS=
-  allow_failures:
-    - os: osx
 
 install:
   - git clone https://github.com/VTest/VTest.git ../vtest