Update C++ namespace snippet to match clang-format

New snippet outputs this

```cpp
namespace {
}  // namespace
```

instead of

```cpp
namespace {
}  // anonymous
```

and this

```cpp
namespace foo {
}  // namespace foo
```

instead of

```cpp
namespace foo {
}  // foo
```

UltiSnips/cpp.snippets

@@ -38,7 +38,7 @@ endsnippet
 snippet namespace "Named or anonymous namespace"
 namespace $1${1/(\w+)/ /}{
 $0
-}  // ${1/(\w*)/(?1:$1:anonymous)/}
+}  // namespace${1/(\w*)/(?1: $1:)/}
 endsnippet
 
 snippet const_cast "Const cast" i