Defaulting env to Ninja in the build matrix
diff --git a/.travis.yml b/.travis.yml
index 993a0d0..7dbfbc5 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -11,10 +11,9 @@
     packages:
     - ninja-build
 
-env:
-  CMAKE_GENERATOR=Ninja
-
 matrix:
+  env:
+    CMAKE_GENERATOR=Ninja
   include:
   - os: linux
     compiler: gcc