Set peachpie platform (#3272)

/cc @roberthusak

frameworks/PHP/peachpie/benchmark_config.json

@@ -17,7 +17,7 @@
       "language": "PHP",
       "flavor": "PHP7",
       "orm": "Raw",
-      "platform": "None",
+      "platform": ".NET",
       "webserver": "None",
       "os": "Linux",
       "database_os": "Linux",