Corrected the func definition for vector emplace

The emplace member function of std::vector should take const_iterator and variadic list of arguments as their input for perfect forwarding (https://en.cppreference.com/w/cpp/container/vector/emplace). This document had rvalue reference instead of variadic list of arguments. I also checked the std::vector implementation MSVC, it is now according to the changes proposed. 
Probably why it still had rvalue reference is explained in this link (https://stackoverflow.com/questions/4303513/push-back-vs-emplace-back).

Author: Pankaj Raghav

docs/standard-library/vector-class.md

@@ -794,18 +794,19 @@ The number '30' is in c1 collection 3 times.
 Inserts an element constructed in place into the vector at a specified position.
 
 ```cpp
+template <class... Types>
 iterator emplace(
     const_iterator _Where,
-    Type&& val);
+    Types&&... _Args);
 ```
 
 ### Parameters
 
 *_Where*\
 The position in the [vector](../standard-library/vector-class.md) where the first element is inserted.
 
-*val*\
-The value of the element being inserted into the `vector`.
+*_Args*\
+Constructor arguments. The function infers which constructor overload to invoke based on the arguments provided.
 
 ### Return Value