🧹 Use git diff --check as another linter

.gitattributes

@@ -0,0 +1,4 @@
+# Trailing spaces may be intentional in markdown documents, so these should not
+# be removed.
+# https://gist.github.com/shaunlebron/746476e6e7a4d698b373
+**/*.md whitespace=-blank-at-eol

CONTRIBUTING.md

@@ -23,9 +23,7 @@ We love pull requests from everyone. By participating in this project, you agree
      `git checkout -b awesome-feature master`
    - Please avoid working [directly on the master branch](https://softwareengineering.stackexchange.com/questions/223400/when-should-i-stop-committing-to-master-on-new-projects).
    - Make commits of logical units.
-- Check for unnecessary whitespace with `git diff --check` before committing.
-   - Note that [two trailing spaces](https://gist.github.com/shaunlebron/746476e6e7a4d698b373) is intentional
-     in markdown documents to create a line break like `<br>`, so these should _not_ be removed.
+- Run script/lint before committing your changes. Fix anything that isn't automatically fixed by the linters.
 - Push your topic branch to your fork and [submit a pull request](https://github.com/mas-cli/mas/compare/master...your-username:topic-branch).
 
 Some things that will increase the chance that your pull request is accepted:

docs/style.md

@@ -1,7 +1,7 @@
 # All Files
 
 - Remove unnecessary whitespace from the end of lines.
-   - Use `git diff --check` to look for these before committing.
+   - Use `script/lint` to look for these before committing.
    - Note that [two trailing spaces](https://gist.github.com/shaunlebron/746476e6e7a4d698b373)
      is intentional in markdown documents to create a line break like `<br>`, so these should _not_ be removed.
 - End each file with a [newline character](https://unix.stackexchange.com/questions/18743/whats-the-point-in-adding-a-new-line-to-the-end-of-a-file#18789).

script/lint

@@ -3,11 +3,14 @@
 # script/lint
 # mas
 #
-# Linting checks for CI "Lint" stage.
+# Linting checks for development and CI.
 #
 
 echo "==> 🚨 Linting mas"
 
+echo "--> 🌳 Git"
+git diff --check
+
 echo
 echo "--> 🕊️ Swift"
 swiftlint lint --strict