[clang-format][docs][NFC] Fix example for Allman brace breaking style

I assume the example is wrong as it's clearly missing line-breaks before
braces.

I just ran the example through clang-format with .clang-format like
this:
BreakBeforeBraces: Allman

Differential Revision: https://reviews.llvm.org/D58941

llvm-svn: 355365