Add dev requirement for subjective-php/psr-cache-mongodb

Author: chadicus

composer.json

@@ -41,7 +41,8 @@
     "require-dev": {
         "php-coveralls/php-coveralls": "^2.1",
         "phpunit/phpunit": "^6.5.2",
-        "squizlabs/php_codesniffer": "^3.2"
+        "squizlabs/php_codesniffer": "^3.2",
+        "subjective-php/psr-cache-mongodb": "^2.1"
     },
     "autoload": {
         "psr-4": { "TraderInteractive\\Api\\": "src" }