new icon: modx (original, original-wordmark, plain, plain-wordmark) (#627)

* Submitting MODX logo

MODX is a popular open source PHP CMS. Its logo is also found in
FontAwesome, seems like it would be great for it to have

* Updated devicon.json and modx svg color

* Fixed issues reported by svg-checker bot

Co-authored-by: JP DeVries <mail@devries.jp>
Co-authored-by: Clemens Bastian <8781699+amacado@users.noreply.github.com>

Author: 3 people

devicon.json

@@ -2220,6 +2220,28 @@
         "color": "#8d6748",
         "aliases": []
     },
+    {
+        "name": "modx",
+        "tags": [
+            "cms",
+            "php",
+            "framework"
+        ],
+        "versions": {
+            "svg": [
+                "original",
+                "original-wordmark",
+                "plain",
+                "plain-wordmark"
+            ],
+            "font": [
+                "plain",
+                "plain-wordmark"
+            ]
+        },
+        "color": "#00decc",
+        "aliases": []
+    },
     {
         "name": "mongodb",
         "tags": [