update logo

README.md

-![mytoken logo](https://git.scc.kit.edu/oidc/mytoken/-/raw/master/docs/img/mytoken.png)
+![mytoken logo](mytoken.png)
 
 [![License](https://img.shields.io/github/license/oidc-mytoken/server.svg)](https://github.com/oidc-mytoken/server/blob/master/LICENSE)
 ![GitHub go.mod Go version](https://img.shields.io/github/go-mod/go-version/oidc-mytoken/server)

internal/server/web/partials/navbar.mustache

 <nav class="navbar navbar-expand-sm navbar-dark bg-primary">
-    <a class="navbar-brand" href="/{{#logged-in}}home{{/logged-in}}"><img src="/static/img/mytoken.png" alt="mytoken" style="height: 50px;"/></a>
+    <a class="navbar-brand" href="/{{#logged-in}}home{{/logged-in}}"><img src="/static/img/mytoken-grey.png"
+                                                                          alt="mytoken" style="height: 50px;"/></a>
     {{^empty-navbar}}
         <ul class="navbar-nav mr-auto">
         </ul>