CI: travis: fix ${TRAVIS_COMMIT_RANGE/.../..}

$TRAVIS_COMMIT_RANGE contains "..." instead of "..", see
travis-ci/travis-ci#4596

Fixes: faadb20 ("CI: travis: new shellcheck-gitrange.bash")

Signed-off-by: Marc Herbert <marc.herbert@intel.com>

.travis.yml

@@ -14,4 +14,7 @@ jobs:
   include:
 
     - name: "shellcheck"
-      script: ./tools/shellcheck-gitrange.bash "${TRAVIS_COMMIT_RANGE}"
+      # $TRAVIS_COMMIT_RANGE contains "..." instead of ".."
+      # https://github.com/travis-ci/travis-ci/issues/4596
+      PR_COMMIT_RANGE="${TRAVIS_COMMIT_RANGE/.../..}"
+      script: ./tools/shellcheck-gitrange.bash "${PR_COMMIT_RANGE}"