Add github-dark theme (#174)

Author: Evavic44

docs/themes/README.md

@@ -73,6 +73,7 @@ You can also try out and customize these themes on the [Demo Site](https://githu
 |       `javascript`     | ![image](https://user-images.githubusercontent.com/62628408/135756315-7a4b8134-8558-4e74-9f24-f8a1a2173b6f.png) |
 |   `javascript-dark`    | ![image](https://user-images.githubusercontent.com/62628408/135761927-a4acd543-c90b-430d-92a3-c96b32bfc390.png) |
 |     `noctis-minimus`   | ![image](https://user-images.githubusercontent.com/20955511/135754306-58ceccde-90d9-46f9-a7b2-1cb54b6fbe24.png) |
+|     `github-dark`      | ![image](https://user-images.githubusercontent.com/62628408/135931624-9e6bf6b8-4965-4c7d-87f6-08217ea9274f.png) |
 ### Can't find the theme you like?
 
 You can now customize your stats card with the interactive [Demo Site](https://github-readme-streak-stats.herokuapp.com/demo/) or by customizing the [url parameters](/README.md#-options).

src/themes.php

@@ -806,4 +806,16 @@
         "sideLabels" => "#d3b692",
         "dates" => "#c5cdd3",
     ],
+    "github-dark" => [
+        "background" => "#0D1117FF",
+        "border" => "#39D353",
+        "stroke" => "#39D353",
+        "ring" => "#39D353",
+        "currStreakNum" => "#FFFFFF",
+        "fire" => "#1F6FEB",
+        "sideNums" => "#FFFFFF",
+        "currStreakLabel" => "#FFFFFF",
+        "sideLabels" => "#FFFFFF",
+        "dates" => "#39D353",
+    ],
 );