Added php.executablePath to package.json contributes.configuration (#105)

package.json

@@ -57,12 +57,22 @@
   },
   "contributes": {
     "configuration": {
+      "type": "object",
+      "title": "PHP IntelliSense",
       "properties": {
         "php.memoryLimit": {
           "type": "string",
           "default": "-1",
           "description": "The memory limit of the php language server. [Number][K|M|G]. Use '-1' to allow unlimited use of the RAM(default).",
           "pattern": "^\\d+[KMG]?$"
+        },
+        "php.executablePath": {
+          "type": [
+            "string",
+            "null"
+          ],
+          "default": null,
+          "description": "The path to a PHP 7+ executable."
         }
       }
     }