message: Add filename to error messages printed from CLI
  This information exists but isn't exposed in the
  error messaging. When run on a big project from
  CLI -- without the filenames, it's difficult to
  track down where the errors are being triggered from.
diff: import { GraphQLError } from 'graphql';
  +import path from 'path';
  // ToolError is used for errors that are part of the expected flow
  // and for which a stack trace should not be printed
  @@ -42,6 +43,11 @@ export function logErrorMessage(message, fileName, lineNumber) {
  console.log(`error: ${message}`);
  }
  } else {
  - console.log(message);
  + if (fileName) {
  + const truncatedFileName = '/' + fileName.split(path.sep).slice(-4).join(path.sep);
  + console.log(`...${truncatedFileName}: ${message}`);
  + } else {
  + console.log(`error: ${message}`);
  + }
  }
  }
  