doc: tweaked x/y axis labeling
doc: tweaked x/y axis labeling

autosportlabs/kivy,janssen/kivy,manthansharma/kivy,jkankiewicz/kivy,bionoid/kivy,manthansharma/kivy,kivy/kivy,jegger/kivy,rafalo1333/kivy,akshayaurora/kivy,jegger/kivy,tony/kivy,autosportlabs/kivy,KeyWeeUsr/kivy,Cheaterman/kivy,kived/kivy,LogicalDash/kivy,LogicalDash/kivy,kived/kivy,jkankiewicz/kivy,LogicalDash/kivy,rnixx/kivy,akshayaurora/kivy,kived/kivy,rnixx/kivy,Cheaterman/kivy,jkankiewicz/kivy,KeyWeeUsr/kivy,bionoid/kivy,rafalo1333/kivy,kivy/kivy,Cheaterman/kivy,inclement/kivy,KeyWeeUsr/kivy,inclement/kivy,jkankiewicz/kivy,matham/kivy,matham/kivy,LogicalDash/kivy,tony/kivy,manthansharma/kivy,matham/kivy,inclement/kivy,Cheaterman/kivy,bionoid/kivy,jegger/kivy,jegger/kivy,akshayaurora/kivy,KeyWeeUsr/kivy,rafalo1333/kivy,autosportlabs/kivy,tony/kivy,kivy/kivy,manthansharma/kivy,matham/kivy,rnixx/kivy,bionoid/kivy,janssen/kivy,janssen/kivy,janssen/kivy