step(info){
    if (info.pc === 0) this.pcZeroCounter++;

    try {
      if (this.validOpcodes[info.opcode.name] && info.stack.length > 0){
        const idx = info.stack.length - 1;
        let hash = '0x' +  info.stack[idx].toString(16);
        this._registerHash(hash);
      }
    } catch (err) { /*Ignore*/ };
  }
VM step event handler. Detects instrumentation hashes when they are pushed to the
top of the stack. This runs millions of times - trying to keep it fast.
@param  {Object} info  vm step info