[llvm-objcopy] [COFF] Fix a typo in a comment. NFC.

  ArrayRef<Section> getSections() const { return Sections; }

  // This allows mutating individual Sections, but not mutating the list

  // of symbols itself.

  // of sections itself.

  iterator_range<std::vector<Section>::iterator> getMutableSections() {

    return make_range(Sections.begin(), Sections.end());

  }