DebugTools: buffer[Sub]Data() relies on ARB_map_buffer_range.

Not sure why this wasn't documented.

src/Magnum/DebugTools/BufferData.h

@@ -53,6 +53,7 @@ Emulates @ref GL::Buffer::subData() call on platforms that don't support it
     @ref MAGNUM_TARGET_GL "TARGET_GL" enabled (done by default). See
     @ref building-features for more information.
 
+@requires_gl30 Extension @gl_extension{ARB,map_buffer_range}
 @requires_gles30 Extension @gl_extension{EXT,map_buffer_range} in OpenGL ES
     2.0.
 @requires_gles Buffer mapping is not available in WebGL.
@@ -73,6 +74,7 @@ as OpenGL ES) by using @ref GL::Buffer::map().
     @ref MAGNUM_TARGET_GL "TARGET_GL" enabled (done by default). See
     @ref building-features for more information.
 
+@requires_gl30 Extension @gl_extension{ARB,map_buffer_range}
 @requires_gles30 Extension @gl_extension{EXT,map_buffer_range} in OpenGL ES
     2.0.
 @requires_gles Buffer mapping is not available in WebGL.