travis: fix codescan fetch head

Author: 0xc0170

.travis.yml

@@ -61,6 +61,9 @@ matrix:
         - pip install scancode-toolkit==3.1.1
       before_script:
         - mkdir -p SCANCODE
+        # Fetch remaining information needed for branch comparison
+        - git fetch --all --unshallow --tags
+        - git fetch origin "${TRAVIS_BRANCH}"
       script:
         # scancode does not support list of files, only one file or directory
         # we use SCANCODE directory for all changed files (their copies with full tree)