Add Mixer (#960)

* Add Mixer
* Changed the source URL

_data/simple-icons.json

@@ -1185,6 +1185,11 @@
             "hex": "314359",
             "source": "https://www.mixcloud.com/branding"
         },
+        {
+            "title": "Mixer",
+            "hex": "002050",
+            "source": "https://github.com/mixer/branding-kit/"
+        },
         {
             "title": "Monero",
             "hex": "FF6600",

icons/mixer.svg

@@ -0,0 +1 @@
+<svg aria-labelledby="simpleicons-mixer-icon" role="img" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><title id="simpleicons-mixer-icon">Mixer icon</title><path d="M2.456 1.375a2.461 2.461 0 0 0-1.65.642C-.134 2.884-.21 4.348.553 5.38l4.917 6.59-4.946 6.65c-.762 1.032-.702 2.496.254 3.363a2.45 2.45 0 0 0 3.617-.344l6.904-9.28a.65.65 0 0 0 0-.763L4.423 2.361a2.432 2.432 0 0 0-1.967-.986zm19.089 0a2.432 2.432 0 0 0-1.968.986l-6.86 9.22a.65.65 0 0 0 0 .762l6.89 9.296a2.45 2.45 0 0 0 3.617.344c.956-.867 1.016-2.331.254-3.363l-4.947-6.65 4.917-6.59c.762-1.032.687-2.496-.254-3.363a2.459 2.459 0 0 0-1.65-.641z"/></svg>