require-dev at least phpunit/phpunit 7.5

Signed-off-by: Jack Cherng <[email protected]>

Author: jfcherng

composer.json

@@ -31,7 +31,7 @@
     "require-dev": {
         "friendsofphp/php-cs-fixer": "^2.14.1",
         "phan/phan": "^1.0",
-        "phpunit/phpunit": "^7.2 || ^8.0",
+        "phpunit/phpunit": "^7.5 || ^8.0",
         "squizlabs/php_codesniffer": "^3.4"
     },
     "config": {