README.md: Refer to proper name for Visual Studio 15

Author: ADKaster

README.md

@@ -82,7 +82,7 @@ Use cmake to build: `cmake -G Ninja . && ninja`
 Run tests after building: `python demumble_test.py`
 
 `cxa_demangle.cpp` needs more C++11 than Visual Studio 2013 supports, so
-to build on Windows you need to use Visual Studion 2015 or use clang-cl
+to build on Windows you need to use Visual Studio 2015 or use clang-cl
 as C++ compiler like so:
 
     cmake -G Ninja -DCMAKE_CXX_COMPILER=path/to/llvm-build/bin/clang-cl.exe