feat: support Storybook 6.4

[zhzz]

Add compatibility with Stroybook 6.4, that has some changes in internal API and story parameters merging strategy.

Improve skip parameter format. Previously you were able define different skip options in one place as an array, you also were able to define another array of skips somewhere else and all these options would be merged in one big array. But Storybook treats arrays as primitive type and since 6.4 it merges global and kind parameters internally. So there is no way to get skips from different parameter levels

diff --git a/src/types.ts b/src/types.ts
index aa24f42..0d3d91c 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -393,16 +393,18 @@ export interface CreeveyStoryParams {
   ignoreElements?: string | string[] | null;
   waitForReady?: boolean;
   delay?: number | { for: string[]; ms: number };
-   skip?: SkipOption | SkipOption[];
+   skip?: SkipOption | SkipOption[] | Record<string, SkipOption | SkipOption[]>;
   tests?: {
     // TODO Define browserName, story
     [name: string]: CreeveyTestFunction;
   };
 }

Now, skip options might be defined as an object with unique keys e.g.:

// MyComponents.stories.tsx
export default {
  title: 'MyComponent'
  parameters: {
    creevey: {
      skip: {
        'MyComponent does not support IE11': { in: 'ie11' },
        'flacky': { stories: ['with Error'] },
      },
    },
  },
};

instead of array:

// MyComponents.stories.tsx
export default {
  title: 'MyComponent'
  parameters: {
    creevey: {
      skip: [
        { in: 'ie11', reason: 'MyComponent does not support IE11' },
        { stories: ['with Error'] },
      ],
    },
  },
};

Note that array can still be used as skip object value:

// preview.tsx
export const parameters = {
  creevey: {
    skip: {
      "flacky": [
        { kinds: ['Button', 'Input'] },
        { stories: 'Loading' },
      ],
    },
  },
};

fix #195