fix(types): make tailwindFunctions and tailwindAttributes optional

[giacomoferretti]

Recently stumbled upon this error, which there is already a workaround here: #161 (comment)

It seems that in #162 these optional arguments were made necessary. See more below.

Before

export interface RawOptions {
  tailwindConfig?: string
  tailwindFunctions?: string[]
  tailwindAttributes?: string[]
}

After

export interface PluginOptions {
  /**
   * Path to the Tailwind config file.
   */
  tailwindConfig?: string

  /**
   * List of custom function and tag names that contain classes.
   */
  tailwindFunctions: string[]

  /**
   * List of custom attributes that contain classes.
   */
  tailwindAttributes: string[]
}

[adamwathan]

Thanks!