#81 - Changed 'rollup-pluginutils' back to '@rollup/pluginutils' plugin and reverted previous code change

[elycruz]

Fixes #81 :

Changes:

• Reverted rollup-pluginutils version back to recently upgraded @rollup/pluginutils version, minus one major version from latest version - The version is set to one major behind to ensure backwards compatibility with existing projects.
  We also upgraded to this version, of @rollup/pluginutils, to allow users, who have started to use rollup-plugin-sass@1.2.5, to continue supplying RegExp | string | string[] for include and exclude properties (rollup-pluginutils doesn't accept RegExp for these props).
• Updated plugin's source to ensure that include and exclude always have a default when their incoming values are directly set to undefined - previous update had removed these default, since they were set in options merge call, however merging in undefined prop. values weren't taken into account in that update - this update fixes that change.
• Downgraded typescript version down to previous major version to ensure we don't output typescript type files that are incompatible with older versions of typescript - it's a good practice to not use the latest typescript version, currently, since some older typescript versions have issues with some of the syntaxes used in later versions of typescript (see: Managing code compatibility in a TypeScript ecosystem with multiple compiler versions microsoft/TypeScript#25778 et al.).