function insertBrace(contract, item, offset) {
  return contract.slice(0,item.pos + offset) + item.type + contract.slice(item.pos + offset)
}
Inserts an open or close brace e.g. `{` or `}` at specified position in solidity source

@param  {String} contract solidity source
@param  {Object} item     AST node to bracket
@param  {Number} offset   tracks the number of previously inserted braces
@return {String}          contract