Fixes #37 Add discussion category action argument.

lib/Inputs.js

@@ -77,6 +77,13 @@ class CoreInputs {
             return undefined;
         return this.name;
     }
+    get discussionCategory() {
+        const category = core.getInput('discussionCategory');
+        if (category) {
+            return category;
+        }
+        return undefined;
+    }
     static get omitName() {
         return core.getInput('omitName') == 'true';
     }