Fix typo in TableGetSortSpecs comment (cpp)

[dimateos]

I ended up in imgui_tables.cpp looking at the implementation for TableGetSortSpecs() and the description is a bit outdated. SpecsChanged is not longer part of the internal (nor external) API.

• Replaced it with an up to date piece from imgui.h
  

  imgui/imgui.h

  Lines 775 to 779 in 82d177c

  	// Tables: Sorting & Miscellaneous functions
  	// - Sorting: call TableGetSortSpecs() to retrieve latest sort specs for the table. NULL when not sorting.
  	// When 'sort_specs->SpecsDirty == true' you should sort your data. It will be true when sorting specs have
  	// changed since last call, or the first time. Make sure to set 'SpecsDirty = false' after sorting,
  	// else you may wastefully sort your data every frame!

  • Correct SpecsChanged -> sort_specs->SpecsDirty
  • Kept the tip about making sure to set 'SpecsDirty = false'

Feel free to edit etc...
Thanks Omar!