function foldLine(line, width) {
  if (line === '' || line[0] === ' ') return line;

  // Since a more-indented line adds a \n, breaks can't be followed by a space.
  var breakRe = / [^ ]/g; // note: the match index will always be <= length-2.
  var match;
  // start is an inclusive index. end, curr, and next are exclusive.
  var start = 0, end, curr = 0, next = 0;
  var result = '';

  // Invariants: 0 <= start <= length-1.
  //   0 <= curr <= next <= max(0, length-2). curr - start <= width.
  // Inside the loop:
  //   A match implies length >= 2, so curr and next are <= length-2.
  while ((match = breakRe.exec(line))) {
    next = match.index;
    // maintain invariant: curr - start <= width
    if (next - start > width) {
      end = (curr > start) ? curr : next; // derive end <= length-2
      result += '\n' + line.slice(start, end);
      // skip the space that was output as \n
      start = end + 1;                    // derive start <= length-1
    }
    curr = next;
  }

  // By the invariants, start <= length-1, so there is something left over.
  // It is either the whole string or a part starting from non-whitespace.
  result += '\n';
  // Insert a break if the remainder is too long and there is a break available.
  if (line.length - start > width && curr > start) {
    result += line.slice(start, curr) + '\n' + line.slice(curr + 1);
  } else {
    result += line.slice(start);
  }

  return result.slice(1); // drop extra \n joiner
}
Merges configuration from defaults/environment variables/overrides and returns
a Probot instance. Finds private key using [`@probot/get-private-key`](https://github.com/probot/get-private-key).

@see https://probot.github.io/docs/configuration/
@param defaults default Options, will be overwritten if according environment variable is set
@param overrides overwrites defaults and according environment variables
@param env defaults to process.env