fix: cheerio issues with HTML serialization

[mnmkng]

After update to cheerio@1.0.0-rc.10 the $.html() calls started failing with the following error:

ERROR CheerioCrawler: Request failed and reached maximum retries {"url":"https://www.example.com/","method":"GET","uniqueKey":"https://www.example.com"}
  TypeError: Cannot read property 'charset' of undefined
      at Object.exports.getAttrList (/Users/mnmkng/Projects/Apify/Actors/bug-test/node_modules/parse5-htmlparser2-tree-adapter/lib/index.js:283:53)
      at Serializer._serializeAttributes (/Users/mnmkng/Projects/Apify/Actors/bug-test/node_modules/parse5/lib/serializer/index.js:99:40)
      at Serializer._serializeElement (/Users/mnmkng/Projects/Apify/Actors/bug-test/node_modules/parse5/lib/serializer/index.js:67:14)
      at Serializer._serializeChildNodes (/Users/mnmkng/Projects/Apify/Actors/bug-test/node_modules/parse5/lib/serializer/index.js:50:26)
      at Serializer._serializeElement (/Users/mnmkng/Projects/Apify/Actors/bug-test/node_modules/parse5/lib/serializer/index.js:93:18)
      at Serializer._serializeChildNodes (/Users/mnmkng/Projects/Apify/Actors/bug-test/node_modules/parse5/lib/serializer/index.js:50:26)
      at Serializer._serializeElement (/Users/mnmkng/Projects/Apify/Actors/bug-test/node_modules/parse5/lib/serializer/index.js:93:18)
      at Serializer._serializeChildNodes (/Users/mnmkng/Projects/Apify/Actors/bug-test/node_modules/parse5/lib/serializer/index.js:50:26)
      at Serializer.serialize (/Users/mnmkng/Projects/Apify/Actors/bug-test/node_modules/parse5/lib/serializer/index.js:36:14)
      at Object.exports.serialize (/Users/mnmkng/Projects/Apify/Actors/bug-test/node_modules/parse5/lib/index.js:28:23)

It's caused by some incompatibility between htmlparser2 which is the streaming parser we use and which was originally used by cheerio and parse5, which is the new parser they use. We can easily override the parser, but not the serializer. It has some sort of compatibility layer, but it seems to be broken and the maintainer of parse5 says he doesn't have time to maintain the library. So let's use this hack to keep using htmlparser2 for serialization too.