Various small tweaks

* Ignore PHPUnit 8.x cache file.
* Only run `composer validate` once per build.
* Ignore the `.git` directory for Parallel Lint to make it faster.

.gitignore

@@ -3,3 +3,4 @@ composer.lock
 .phpcs.xml
 phpcs.xml
 phpunit.xml
+.phpunit.result.cache

.travis.yml

@@ -61,6 +61,9 @@ jobs:
         - diff -B ./PHPCSDebug/ruleset.xml <(xmllint --format "./PHPCSDebug/ruleset.xml")
         - diff -B ./PHPCSDev/ruleset.xml <(xmllint --format "./PHPCSDev/ruleset.xml")
 
+        # Validate the composer.json file.
+        # @link https://getcomposer.org/doc/03-cli.md#validate
+        - composer validate --no-check-all --strict
 
     #### QUICK TEST STAGE ####
     # This is a much quicker test which only runs the unit tests and linting against the low/high
@@ -144,9 +147,5 @@ script:
   # which is why it is run against various PHP versions and not in the "Sniff" stage.
   - if [[ "$LINT" == "1" ]]; then composer check-complete; fi
 
-  # Validate the composer.json file.
-  # @link https://getcomposer.org/doc/03-cli.md#validate
-  - if [[ "$LINT" == "1" ]]; then composer validate --no-check-all --strict; fi
-
   # Run the unit tests.
   - if [[ $PHPCS_VERSION != "n/a" ]]; then composer run-tests; fi

composer.json

@@ -36,7 +36,7 @@
     ],
     "scripts" : {
         "lint": [
-            "@php ./vendor/jakub-onderka/php-parallel-lint/parallel-lint . -e php --exclude vendor"
+            "@php ./vendor/jakub-onderka/php-parallel-lint/parallel-lint . -e php --exclude vendor --exclude .git"
         ],
         "check-cs": [
             "@php ./vendor/squizlabs/php_codesniffer/bin/phpcs"