Test sdist on release* branch. Directly otherwise

.travis.yml

@@ -42,18 +42,19 @@ install:
 
 script:
   - cabal check
+  - |
+  case "$TRAVIS_BRANCH" of
+  "release"*)
+    touch ChangeLog
+    sdistdir="$TRAVIS_BUILD_DIR/../sdist-test"
+    mkdir -p "$sdistdir"
+    tar zvxf $(stack sdist 2>&1 | tail -n1 | sed 's/.* //') --strip-components=1 -C "$sdistdir"
+    cp "ghc-$GHCVER.yaml" stack.yaml "$sdistdir"
+    cd "$sdistdir"
+    ;;
+  esac
   - stack --no-terminal build --test --no-run-tests
   - stack --no-terminal test ghc-mod:spec
-  - |
-    if [ -r "$TRAVIS_BUILD_DIR/ChangeLog" ]; then
-      sdistdir="$TRAVIS_BUILD_DIR/../sdist-test"
-      mkdir -p "$sdistdir"
-      tar zvxf $(stack sdist 2>&1 | tail -n1 | sed 's/.* //') --strip-components=1 -C "$sdistdir"
-      cp "ghc-$GHCVER.yaml" stack.yaml "$sdistdir"
-      cd "$sdistdir"
-      stack --no-terminal build --test --no-run-tests
-      stack --no-terminal test ghc-mod:spec
-    fi
 
 matrix:
   matrix: