[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

docs/YamlIO.rst

@@ -1020,7 +1020,7 @@ object.  For example:
      // Reading multiple documents in one file
      using llvm::yaml::Input;
 
-     LLVM_YAML_IS_DOCUMENT_LIST_VECTOR(std::vector<MyDocType>)
+     LLVM_YAML_IS_DOCUMENT_LIST_VECTOR(MyDocType)
      
      Input yin(mb.getBuffer());