[Development] typo in docs

[Thomas Zander]

hey,

just sending a quick email because I detected a typo in qpainter.cpp which 
misspells an enum value. So copy paste gave me a compile error :)
It would be much appreciated if someone that actually has push rights changes 
this and pushes it upstream, since creating a merge request is kinda overkill.

Thanks!

hunk src/gui/painting/qpainter.cpp 2259
-    \l {QImage::Format}{Format_ARGB32Premultiplied} or
+    \l {QImage::Format}{Format_ARGB32_Premultiplied} or

-- 
Thomas Zander