inc method
Increments the value of the field by the specified amount.
Implementation
ModifierBuilder inc(String fieldName, value) {
  _updateOperation('\$inc', fieldName, value);
  return this;
}Increments the value of the field by the specified amount.
ModifierBuilder inc(String fieldName, value) {
  _updateOperation('\$inc', fieldName, value);
  return this;
}