Formatter removes mutates keyword

[anton-trunov]

The formatter would remove the mutates keyword from all of the functions. For instance, the following snippet

struct Array {
    m: map<Int as uint16, Int>;
    length: Int = 0;
}

const MaxArraySize: Int = 5_000;

extends mutates fun append(self: Array, item: Int) {
    require(self.length + 1 <= MaxArraySize, "No space in the array left for new items!");

    self.m.set(self.length, item);
    self.length += 1;
}

gets formatted as

struct Array {
  m: map<Int as uint16, Int>;
  length: Int = 0;
}
const MaxArraySize: Int = 5000;

extends fun append(self: Array, item: Int) {
  require((self.length + 1) <= MaxArraySize,
    "No space in the array left for new items!"
  );
  self.m.set(self.length, item);
  self.length += 1;
}