Modified TravisCI script in order to get the latest Shellcheck

Author: frenck

.travis.yml

@@ -12,8 +12,14 @@ env:
     - PATH="${HOME}/bin:${PATH}"
     - SHELLCHECK_URL="https://s3.amazonaws.com/travis-blue-public/binaries/ubuntu/14.04/x86_64/shellcheck-0.4.5.tar.bz2"
 
+cache:
+  directories:
+  - "${HOME}/bin"
+
 before_install:
-    - curl -sSL "${SHELLCHECK_URL}" | tar --exclude 'SHA256SUMS' --strip-components=1 -C "${HOME}/bin" -xjf -;
+    - if ! shellcheck --version ; then
+        curl -sSL "${SHELLCHECK_URL}" | tar -C "${HOME}/bin" -xjf - ;
+      fi
     - shellcheck --version
     - gpg --keyserver hkp://keys.gnupg.net --recv-keys C4133165DF5EB4BAEABDADCACF1E7823C5339B59