prefer stable for pull request CI

Author: cuviper

.travis.yml

@@ -9,7 +9,7 @@ matrix:
   fast_finish: true
   include:
     # NB: To help with CI delays, each `pull_request` is only tested on Linux,
-    # with 1.13 for compatibility and nightly+rayon_unstable for broad test
+    # with 1.13 for compatibility and stable+rayon_unstable for broad test
     # coverage.  The bors bot counts as a `push` type, which will run it all.
 
     - rust: 1.13.0
@@ -29,7 +29,7 @@ matrix:
     - rust: stable
       os: linux
       env: RUSTFLAGS='--cfg rayon_unstable'
-      if: NOT type = pull_request
+      #if: everything!
 
     - rust: beta
       os: linux
@@ -45,7 +45,7 @@ matrix:
     - rust: nightly
       os: linux
       env: RUSTFLAGS='--cfg rayon_unstable'
-      #if: everything!
+      if: NOT type = pull_request
 
     - rust: stable
       os: osx