radiant -> radians

Co-authored-by: Bart Louwers <bart.louwers@gmail.com>

Author: Murmele

src/mbgl/map/transform.cpp

@@ -514,7 +514,7 @@ void Transform::rotateBy(double angleDegree, const AnimationOptions& animation)
 /*!
  * \brief Transform::getBearing
  * Bearing in radiant
- * \return
+ * \return bearing in radians
  */
 double Transform::getBearing() const {
     return state.getBearing();