travis: Use latest shellcheck

.travis.yml

@@ -9,6 +9,14 @@ before_install:
     - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew update; fi
     - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew install screenresolution; fi
 
+install:
+  # Install a custom version of shellcheck instead of Travis CI's default
+  - scversion="latest" # or "v0.4.7", or "latest"
+  - wget "https://storage.googleapis.com/shellcheck/shellcheck-${scversion}.linux.x86_64.tar.xz"
+  - tar --xz -xvf "shellcheck-${scversion}.linux.x86_64.tar.xz"
+  - shellcheck() { "shellcheck-${scversion}/shellcheck" "$@"; }
+  - shellcheck --version
+
 script:
     - time ./neofetch --travis -v
     - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then shellcheck neofetch; fi