add support for custom mutation name

src/Observer.js

@@ -15,6 +15,7 @@ export default class {
     this.connect(connectionUrl, opts)
 
     if (opts.store) { this.store = opts.store }
+    if (opts.mutations) { this.mutations = opts.mutations }
     this.onEvent()
   }
 
@@ -74,6 +75,10 @@ export default class {
         target = [msg.namespace || '', msg.action].filter((e) => !!e).join('/')
       }
     }
-    this.store[method](target, msg)
+    if (this.mutations) {
+        this.store[this.mutations[method] || method](target, msg)
+    } else {
+        this.store[method](target, msg)
+    }
   }
 }