clang-format: Improve formatting of ObjC array literals.

Before:
  NSArray *arguments =
      @[ kind == kUserTicket ? @"--user-store" : @"--system-store",
         @"--print-tickets", @"--productid", @"com.google.Chrome" ];
After:
  NSArray *arguments = @[
      kind == kUserTicket ? @"--user-store" : @"--system-store",
      @"--print-tickets",
      @"--productid",
      @"com.google.Chrome"
  ];

This fixes llvm.org/PR15231.