travis: Correctly process $SOURCE_CHECK_ONLY.

The `!` outside of parentheses was being cut by travis.

.travis.yml

@@ -6,7 +6,7 @@ notifications:
   email: false
 
 env:
-  - SOURCE_CHECK_ONLY=true
+  - ARCH=32 SOURCE_CHECK_ONLY=true
   - NO_VALGRIND=1 ARCH=32 DEVELOPER=1 COMPILER=gcc TEST_GROUP=1 TEST_GROUP_COUNT=2 SOURCE_CHECK_ONLY=false
   - NO_VALGRIND=1 ARCH=32 DEVELOPER=1 COMPILER=gcc TEST_GROUP=2 TEST_GROUP_COUNT=2 SOURCE_CHECK_ONLY=false
   - NO_VALGRIND=1 ARCH=64 DEVELOPER=1 COMPILER=gcc SOURCE_CHECK_ONLY=false
@@ -27,6 +27,6 @@ script:
   - env | grep -E '^[A-Z_]+\=' | tee /tmp/envlist
   - $SOURCE_CHECK_ONLY || docker run --rm=true -v "${TRAVIS_BUILD_DIR}":/build -t cdecker/lightning-ci:${ARCH}bit make -j3 CC=${COMPILER} DEVELOPER=${DEVELOPER}
   - $SOURCE_CHECK_ONLY || docker run --rm=true --env-file=/tmp/envlist -v "${TRAVIS_BUILD_DIR}":/build -t cdecker/lightning-ci:${ARCH}bit make CC=${COMPILER} check DEVELOPER=${DEVELOPER}
-#  - ! $SOURCE_CHECK_ONLY || git clone https://github.com/lightningnetwork/lightning-rfc.git
-#  - ! $SOURCE_CHECK_ONLY || docker run --rm=true -v "${TRAVIS_BUILD_DIR}":/build -t cdecker/lightning-ci:${ARCH}bit make check-source BOLTDIR=lightning-rfc
-  - ! $SOURCE_CHECK_ONLY || docker run --rm=true -v "${TRAVIS_BUILD_DIR}":/build -t cdecker/lightning-ci:${ARCH}bit make check-source BOLTDIR=none
+#  - (! $SOURCE_CHECK_ONLY) || git clone https://github.com/lightningnetwork/lightning-rfc.git
+#  - (! $SOURCE_CHECK_ONLY) || docker run --rm=true -v "${TRAVIS_BUILD_DIR}":/build -t cdecker/lightning-ci:${ARCH}bit make check-source BOLTDIR=lightning-rfc
+  - (! $SOURCE_CHECK_ONLY) || docker run --rm=true -v "${TRAVIS_BUILD_DIR}":/build -t cdecker/lightning-ci:${ARCH}bit make check-source BOLTDIR=none