Test only specified rules

Author: SaschaMann

.github/markdownlint.json

@@ -1,6 +1,6 @@
 {
-    "default": true,
-    "heading-style": "atx",
-    "line_length": false,
-    "no-inline-html": false
+    "default": false,
+    "heading-increment": true,
+    "first-line-heading": true,
+    "heading-style": "atx"
 }