emacs: Fix a warning
emacs: Fix a warning

Fix a following byte-compile warning:
ninja-mode.el:18:7:Warning: assignment to free variable `ninja-keywords'

AoD314/ninja,atetubou/ninja,Maratyszcza/ninja-pypi,sxlin/dist_ninja,dendy/ninja,ignatenkobrain/ninja,metti/ninja,drbo/ninja,martine/ninja,guiquanz/ninja,sxlin/dist_ninja,colincross/ninja,Ju2ender/ninja,automeka/ninja,purcell/ninja,Maratyszcza/ninja-pypi,nocnokneo/ninja,Ju2ender/ninja,mohamed/ninja,glensc/ninja,iwadon/ninja,mydongistiny/ninja,nicolasdespres/ninja,sxlin/dist_ninja,ninja-build/ninja,Qix-/ninja,synaptek/ninja,kissthink/ninja,juntalis/ninja,ignatenkobrain/ninja,ndsol/subninja,mohamed/ninja,sxlin/dist_ninja,martine/ninja,rjogrady/ninja,ThiagoGarciaAlves/ninja,drbo/ninja,ilor/ninja,rjogrady/ninja,ctiller/ninja,vvvrrooomm/ninja,mgaunard/ninja,Maratyszcza/ninja-pypi,nafest/ninja,automeka/ninja,moroten/ninja,Ju2ender/ninja,mohamed/ninja,mgaunard/ninja,ndsol/subninja,fuchsia-mirror/third_party-ninja,rjogrady/ninja,ilor/ninja,purcell/ninja,glensc/ninja,moroten/ninja,colincross/ninja,sorbits/ninja,Qix-/ninja,purcell/ninja,fuchsia-mirror/third_party-ninja,fuchsia-mirror/third_party-ninja,tfarina/ninja,ignatenkobrain/ninja,AoD314/ninja,dorgonman/ninja,atetubou/ninja,bmeurer/ninja,jhanssen/ninja,sorbits/ninja,jendrikillner/ninja,vvvrrooomm/ninja,jendrikillner/ninja,purcell/ninja,bmeurer/ninja,metti/ninja,mydongistiny/ninja,nocnokneo/ninja,sorbits/ninja,kissthink/ninja,ignatenkobrain/ninja,glensc/ninja,Qix-/ninja,autopulated/ninja,ilor/ninja,synaptek/ninja,sxlin/dist_ninja,ctiller/ninja,glensc/ninja,drbo/ninja,martine/ninja,syntheticpp/ninja,hnney/ninja,tfarina/ninja,iwadon/ninja,lizh06/ninja,dendy/ninja,mydongistiny/ninja,mgaunard/ninja,jhanssen/ninja,atetubou/ninja,synaptek/ninja,bradking/ninja,maruel/ninja,nicolasdespres/ninja,liukd/ninja,Ju2ender/ninja,dorgonman/ninja,jimon/ninja,ninja-build/ninja,bradking/ninja,ndsol/subninja,martine/ninja,hnney/ninja,mydongistiny/ninja,sgraham/ninja,kissthink/ninja,lizh06/ninja,guiquanz/ninja,ninja-build/ninja,juntalis/ninja,mohamed/ninja,liukd/ninja,lizh06/ninja,vvvrrooomm/ninja,atetubou/ninja,synaptek/ninja,guiquanz/ninja,jendrikillner/ninja,sxlin/dist_ninja,bmeurer/ninja,syntheticpp/ninja,kissthink/ninja,maruel/ninja,drbo/ninja,nafest/ninja,liukd/ninja,iwadon/ninja,jimon/ninja,nico/ninja,hnney/ninja,sgraham/ninja,nicolasdespres/ninja,sgraham/ninja,nocnokneo/ninja,guiquanz/ninja,nafest/ninja,sxlin/dist_ninja,jhanssen/ninja,jendrikillner/ninja,mgaunard/ninja,dendy/ninja,AoD314/ninja,vvvrrooomm/ninja,juntalis/ninja,maruel/ninja,syntheticpp/ninja,metti/ninja,moroten/ninja,moroten/ninja,Maratyszcza/ninja-pypi,iwadon/ninja,tfarina/ninja,automeka/ninja,metti/ninja,dorgonman/ninja,AoD314/ninja,juntalis/ninja,autopulated/ninja,dendy/ninja,syntheticpp/ninja,ninja-build/ninja,fuchsia-mirror/third_party-ninja,liukd/ninja,jhanssen/ninja,colincross/ninja,bmeurer/ninja,ndsol/subninja,nicolasdespres/ninja,autopulated/ninja,ilor/ninja,ThiagoGarciaAlves/ninja,ctiller/ninja,nico/ninja,nafest/ninja,hnney/ninja,dorgonman/ninja,tfarina/ninja,ctiller/ninja,rjogrady/ninja,nico/ninja,nico/ninja,nocnokneo/ninja,automeka/ninja,sgraham/ninja,ThiagoGarciaAlves/ninja,maruel/ninja,sorbits/ninja,bradking/ninja,ThiagoGarciaAlves/ninja,jimon/ninja,Qix-/ninja,jimon/ninja,colincross/ninja,lizh06/ninja,bradking/ninja,autopulated/ninja