feat(supported-version): validate custom_versions

Previously, @danslo reported that he tried to use `custom_versions` without
setting the kind. This isn't the correct behavior.
I've added a validator to alert him of this.

supported-version/src/index.ts

@@ -1,15 +1,15 @@
 import * as core from '@actions/core';
-import { validateOrError } from './kind/compute-kind';
+import { validateKind } from './kind/validate-kinds';
 import { getMatrixForKind } from './matrix/get-matrix-for-kind';
 
 
 export async function run(): Promise<void> {
   try { 
     const kind = core.getInput("kind");
-    validateOrError(kind);
-
     const customVersions = core.getInput("custom_versions");
 
+    validateKind(<any>kind, customVersions.split(','));
+
     core.setOutput('matrix', getMatrixForKind(kind, customVersions));
   } 
   catch (error) {