DOC: fix var. reference in percentile docstring
DOC: fix var. reference in percentile docstring

The argument for the original input array is named `a`
but in the docstring it was at some point referred to as `arr`.

[skip ci]

simongibbons/numpy,dwillmer/numpy,MSeifert04/numpy,pizzathief/numpy,dwillmer/numpy,seberg/numpy,b-carter/numpy,ahaldane/numpy,mhvk/numpy,seberg/numpy,jonathanunderwood/numpy,mhvk/numpy,kiwifb/numpy,skwbc/numpy,ChristopherHogan/numpy,seberg/numpy,ahaldane/numpy,cjermain/numpy,nbeaver/numpy,behzadnouri/numpy,numpy/numpy,behzadnouri/numpy,skwbc/numpy,gfyoung/numpy,maniteja123/numpy,ahaldane/numpy,charris/numpy,WillieMaddox/numpy,endolith/numpy,Dapid/numpy,chatcannon/numpy,tacaswell/numpy,joferkington/numpy,cjermain/numpy,abalkin/numpy,behzadnouri/numpy,shoyer/numpy,madphysicist/numpy,Eric89GXL/numpy,pdebuyl/numpy,joferkington/numpy,mhvk/numpy,bertrand-l/numpy,rherault-insa/numpy,ssanderson/numpy,ViralLeadership/numpy,ahaldane/numpy,anntzer/numpy,WarrenWeckesser/numpy,WarrenWeckesser/numpy,skwbc/numpy,jakirkham/numpy,ESSS/numpy,mwiebe/numpy,stuarteberg/numpy,argriffing/numpy,utke1/numpy,rgommers/numpy,jakirkham/numpy,leifdenby/numpy,jorisvandenbossche/numpy,MSeifert04/numpy,pdebuyl/numpy,simongibbons/numpy,numpy/numpy,moreati/numpy,anntzer/numpy,grlee77/numpy,nbeaver/numpy,tynn/numpy,chatcannon/numpy,mhvk/numpy,pizzathief/numpy,gmcastil/numpy,chiffa/numpy,shoyer/numpy,SiccarPoint/numpy,SiccarPoint/numpy,madphysicist/numpy,WillieMaddox/numpy,groutr/numpy,bertrand-l/numpy,shoyer/numpy,jonathanunderwood/numpy,endolith/numpy,grlee77/numpy,dwillmer/numpy,tynn/numpy,groutr/numpy,shoyer/numpy,tacaswell/numpy,pizzathief/numpy,ContinuumIO/numpy,abalkin/numpy,moreati/numpy,numpy/numpy,njase/numpy,SiccarPoint/numpy,solarjoe/numpy,madphysicist/numpy,rgommers/numpy,abalkin/numpy,madphysicist/numpy,b-carter/numpy,maniteja123/numpy,shoyer/numpy,Dapid/numpy,ESSS/numpy,pbrod/numpy,bringingheavendown/numpy,ssanderson/numpy,rherault-insa/numpy,seberg/numpy,ContinuumIO/numpy,ChristopherHogan/numpy,kiwifb/numpy,pbrod/numpy,bertrand-l/numpy,rgommers/numpy,pdebuyl/numpy,stuarteberg/numpy,jakirkham/numpy,mattip/numpy,pyparallel/numpy,rherault-insa/numpy,cjermain/numpy,grlee77/numpy,mwiebe/numpy,anntzer/numpy,pbrod/numpy,SiccarPoint/numpy,cjermain/numpy,MSeifert04/numpy,chiffa/numpy,joferkington/numpy,rgommers/numpy,drasmuss/numpy,njase/numpy,Eric89GXL/numpy,Dapid/numpy,Eric89GXL/numpy,pizzathief/numpy,AustereCuriosity/numpy,Eric89GXL/numpy,chatcannon/numpy,joferkington/numpy,jorisvandenbossche/numpy,pizzathief/numpy,numpy/numpy,MSeifert04/numpy,utke1/numpy,AustereCuriosity/numpy,mhvk/numpy,chiffa/numpy,pyparallel/numpy,mattip/numpy,pbrod/numpy,ViralLeadership/numpy,charris/numpy,gfyoung/numpy,ddasilva/numpy,stuarteberg/numpy,bringingheavendown/numpy,moreati/numpy,argriffing/numpy,grlee77/numpy,leifdenby/numpy,gmcastil/numpy,WarrenWeckesser/numpy,grlee77/numpy,AustereCuriosity/numpy,tynn/numpy,leifdenby/numpy,ViralLeadership/numpy,bringingheavendown/numpy,simongibbons/numpy,WarrenWeckesser/numpy,ChristopherHogan/numpy,madphysicist/numpy,jorisvandenbossche/numpy,endolith/numpy,solarjoe/numpy,pyparallel/numpy,mattip/numpy,ahaldane/numpy,drasmuss/numpy,njase/numpy,endolith/numpy,kiwifb/numpy,MSeifert04/numpy,maniteja123/numpy,pdebuyl/numpy,mattip/numpy,ddasilva/numpy,ChristopherHogan/numpy,mwiebe/numpy,simongibbons/numpy,jonathanunderwood/numpy,ESSS/numpy,groutr/numpy,ssanderson/numpy,charris/numpy,charris/numpy,b-carter/numpy,tacaswell/numpy,argriffing/numpy,gfyoung/numpy,anntzer/numpy,drasmuss/numpy,stuarteberg/numpy,solarjoe/numpy,simongibbons/numpy,nbeaver/numpy,jakirkham/numpy,WillieMaddox/numpy,jorisvandenbossche/numpy,pbrod/numpy,WarrenWeckesser/numpy,jakirkham/numpy,ContinuumIO/numpy,dwillmer/numpy,utke1/numpy,ddasilva/numpy,jorisvandenbossche/numpy,gmcastil/numpy