added missing gasPrice value to transaction

and a note that it's required

Fixed typos in README.md Usage instructions code example that cause an errors when executed

Fixed missing "new" flag in Usage instructions

Fixed typo in Usage instructions that caused an Uncaught Error: [ethjs-provider-http] the HttpProvider instance requires the "new" flag in order to function normally (e.g. `const eth = new Eth(new HttpProvider());`).