chore(config): make smtp provider the default for dev env

https://github.com/mozilla/fxa-email-service/pull/126
r=philbooth

config/dev.json

@@ -1,3 +1,7 @@
 {
-  "logging": "pretty"
+  "logging": "pretty",
+  "provider": "smtp",
+  "smtp": {
+    "port": 9999
+  }
 }