v4.0.20200531

• [Blob.js] Do not attempt to set readonly property Symbols (@bjornstar)
• [Blob.js] Do not use prototype built-ins (@bjornstar)
• [.travis.yml] Drop testing for node v6 and v8 (@bjornstar)
• [.travis.yml] Add testing for node v14 (@bjornstar)
• [package.json] Update devDependencies: eslint & mocha (@bjornstar)
• [.gitignore] Add npm-debug.log (@bjornstar)
• [README] Add usage examples to encourage non-global use of Blob (@bjornstar)