Correct JSON MIME type (Fixes #393)

plugin/web.py

@@ -248,7 +248,7 @@ def allowOrigin(self, req):
     def buildHeaders(self, corsOrigin, body):
         return [
             ['HTTP/1.1 200 OK', None],
-            ['Content-Type', 'text/json'],
+            ['Content-Type', 'application/json'],
             ['Access-Control-Allow-Origin', corsOrigin],
             ['Access-Control-Allow-Headers', '*'],
             ['Content-Length', str(len(body))]
@@ -298,4 +298,4 @@ def format_exception_reply(_api_version, exception):
         "params": {"type": "object"},
     },
     "required": ["action"],
-}
+}