[PSR] Fixed library source

- Using `php-cs-fixer` tool.

lib/PayPal/Validation/ArgumentValidator.php

@@ -23,7 +23,7 @@ class ArgumentValidator
         if ($argument === null) {
             // Error if Object Null
             throw new \InvalidArgumentException("$argumentName cannot be null");
-        } else if (gettype($argument) == 'string' && trim($argument) == ''){
+        } elseif (gettype($argument) == 'string' && trim($argument) == '') {
             // Error if String Empty
             throw new \InvalidArgumentException("$argumentName string cannot be empty");
         }

lib/PayPal/Validation/JsonValidator.php

@@ -32,4 +32,4 @@ class JsonValidator
         }
         return true;
     }
-} 
+}

lib/PayPal/Validation/NumericValidator.php

@@ -21,7 +21,6 @@ class NumericValidator
     {
         if (trim($argument) != null && !is_numeric($argument)) {
             throw new \InvalidArgumentException("$argumentName is not a valid numeric value");
-
         }
         return true;
     }

lib/PayPal/Validation/UrlValidator.php

@@ -23,4 +23,4 @@ class UrlValidator
             throw new \InvalidArgumentException("$urlName is not a fully qualified URL");
         }
     }
-}
+}