fix github font version and add alias

as reported in issue #373 github font is saved as original but the devicon.json is referencing the non-existing plain version

Author: amacado

devicon.json

@@ -1105,12 +1105,17 @@
                 "original-wordmark"
             ],
             "font": [
-                "plain",
-                "plain-wordmark"
+                "original",
+                "original-wordmark"
             ]
         },
         "color": "#181616",
-        "aliases": []
+        "aliases": [
+            {
+                "base": "original",
+                "alias": "plain"
+            }
+        ]
     },
     {
         "name": "gitlab",
@@ -2952,4 +2957,4 @@
         "color": "#68b604",
         "aliases": []
     }
-]
+]