fix typo in color documentation
In `ImColor` was renamed to `ImColor32`.
The documentation in color.rs appears to be wrong, so we fix it.
/// bytes). For clarity: we don't support an equivalent to the
/// `IMGUI_USE_BGRA_PACKED_COLOR` define.
///
-/// This used to be named `ImColor32`, but was renamed to avoid confusion with
+/// This used to be named `ImColor`, but was renamed to avoid confusion with
/// the type with that name in the C++ API (which uses 32 bits per channel).
///
/// While it doesn't provide methods to access the fields, they can be accessed
