Use composer to install PHPCS and friends on Travis

.travis.yml

@@ -48,19 +48,10 @@ matrix:
 before_script:
     # Speed up build time by disabling Xdebug.
     - phpenv config-rm xdebug.ini || echo 'No xdebug config.'
-    # Set up temporary paths.
-    - export PHPCS_DIR=/tmp/phpcs
-    - export WPCS_DIR=/tmp/wpcs
-    - export PHPCOMPAT_DIR=/tmp/phpcompatibility
-    # Install CodeSniffer for WordPress Coding Standards checks.
-    - if [[ "$SNIFF" == "1" ]]; then git clone -b master --depth 1 https://github.com/squizlabs/PHP_CodeSniffer.git $PHPCS_DIR; fi
-    # Install WordPress Coding Standards.
-    - if [[ "$SNIFF" == "1" ]]; then git clone -b 0.14.1 --depth 1 https://github.com/WordPress-Coding-Standards/WordPress-Coding-Standards.git $WPCS_DIR; fi
-    # Install PHP Compatibility sniffs.
-    - if [[ "$SNIFF" == "1" ]]; then git clone -b master --depth 1 https://github.com/wimg/PHPCompatibility.git $PHPCOMPAT_DIR; fi
-    # Set install path for PHPCS sniffs.
-    # @link https://github.com/squizlabs/PHP_CodeSniffer/blob/4237c2fc98cc838730b76ee9cee316f99286a2a7/CodeSniffer.php#L1941
-    - if [[ "$SNIFF" == "1" ]]; then $PHPCS_DIR/bin/phpcs --config-set installed_paths $WPCS_DIR,$PHPCOMPAT_DIR; fi
+    # Install WordPress Coding Standards & PHP Compatibility sniffs.
+    - if [[ "$SNIFF" == "1" ]]; then composer global require wp-coding-standards/wpcs:~0.14.1 wimg/php-compatibility:dev-master dealerdirect/phpcodesniffer-composer-installer:^0.4.3 --prefer-stable --no-interaction --no-suggest; fi
+    # Set composer PATH.
+    - if [[ "$SNIFF" == "1" ]]; then export PATH=$HOME/.composer/vendor/bin:$PATH; fi
     # After CodeSniffer install you should refresh your path.
     - if [[ "$SNIFF" == "1" ]]; then phpenv rehash; fi
     # Install JSCS: JavaScript Code Style checker.
@@ -87,7 +78,7 @@ script:
     # @link https://pear.php.net/package/PHP_CodeSniffer/
     # Uses a custom ruleset based on WordPress. This ruleset is automatically
     # picked up by PHPCS as it's named `phpcs.xml(.dist)`.
-    - if [[ "$SNIFF" == "1" ]]; then $PHPCS_DIR/bin/phpcs --runtime-set ignore_warnings_on_exit 1; fi
+    - if [[ "$SNIFF" == "1" ]]; then phpcs --runtime-set ignore_warnings_on_exit 1; fi
 
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 # @link https://docs.travis-ci.com/user/notifications/#Email-notifications