Merge pull request #275 from testwill/typo

fix: efficient typo

README.md

@@ -512,7 +512,7 @@ linking your middleware if you have built one:
 | [onthefly](https://github.com/xyproto/onthefly)                              | [Alexander Rødseth](https://github.com/xyproto)      | Generate TinySVG, HTML and CSS on the fly                                                                                       |
 | [permissions2](https://github.com/xyproto/permissions2)                      | [Alexander Rødseth](https://github.com/xyproto)      | Cookies, users and permissions                                                                                                  |
 | [prometheus](https://github.com/zbindenren/negroni-prometheus)               | [Rene Zbinden](https://github.com/zbindenren)        | Easily create metrics endpoint for the [prometheus](http://prometheus.io) instrumentation tool                                  |
-| [prometheus](https://github.com/slok/go-prometheus-middleware)               | [Xabier Larrakoetxea](https://github.com/slok)       | [Prometheus](http://prometheus.io) metrics with multiple options that follow standards and try to be measured in a efficent way |
+| [prometheus](https://github.com/slok/go-prometheus-middleware)               | [Xabier Larrakoetxea](https://github.com/slok)       | [Prometheus](http://prometheus.io) metrics with multiple options that follow standards and try to be measured in a efficient way |
 | [render](https://github.com/unrolled/render)                                 | [Cory Jacobsen](https://github.com/unrolled)         | Render JSON, XML and HTML templates                                                                                             |
 | [RestGate](https://github.com/pjebs/restgate)                                | [Prasanga Siripala](https://github.com/pjebs)        | Secure authentication for REST API endpoints                                                                                    |
 | [secure](https://github.com/unrolled/secure)                                 | [Cory Jacobsen](https://github.com/unrolled)         | Middleware that implements a few quick security wins                                                                            |