[Docs] Fix LLVM_YAML_IS_DOCUMENT_LIST_VECTOR

The docs incorrectly said to repeat std::vector inside
LLVM_YAML_IS_DOCUMENT_LIST_VECTOR.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@337695 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed