Travis: re-enable gcov build

.travis.yml

@@ -51,21 +51,13 @@ compiler:
     - gcc
 
 matrix:
-    # Don't build on OS X with gcc
+    include:
+      - os: linux
+        compiler: gcc
+        env: COVERAGE=--enable-gcov
     exclude:
       - os: osx
         compiler: gcc
-    # Add a gcov build (XXX not yet; allows_failures doesn't match
-    # explicitly included rows)
-    #include:
-    #    - compiler: gcc
-    #      env: COVERAGE="--enable-gcov"
-    #      os: linux
-    # The gcov build is not working quite yet
-    #allow_failures:
-    #    compiler: gcc
-    #    env: COVERAGE="--enable-gcov"
-    #    os: linux
 
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