Update Pixel.js and Diva.js

[jackyyzhang03]

• Update Pixel.js submodule to be up to date with master
• Update Diva.js to 6.0.2 as required by new Pixel.js version
• Remove linting of source files in Gulp as it should be done in Pixel.js or Diva.js, as any issues during linting prevent the wrapper from being built, even though we cannot fix them inside the wrapper repo