fix(frontends/lean/definition_cmds): create theorem when keyword 'theorem' is used
fix(frontends/lean/definition_cmds): create theorem when keyword 'theorem' is used

dselsam/lean,rlewis1988/lean,fgdorais/lean,fgdorais/lean,dselsam/lean,digama0/lean,leanprover-community/lean,leodemoura/lean,johoelzl/lean,leanprover/lean,leodemoura/lean,leanprover-community/lean,fpvandoorn/lean,fgdorais/lean,leanprover-community/lean,avigad/lean,johoelzl/lean,leanprover-community/lean,digama0/lean,fpvandoorn/lean,dselsam/lean,dselsam/lean,leanprover/lean,soonhokong/lean-windows,leodemoura/lean,Kha/lean,digama0/lean,fpvandoorn/lean,soonhokong/lean-osx,rlewis1988/lean,johoelzl/lean,fgdorais/lean,soonhokong/lean-windows,avigad/lean,digama0/lean,johoelzl/lean,soonhokong/lean-windows,dselsam/lean,soonhokong/lean-osx,leanprover/lean,Kha/lean,leodemoura/lean,digama0/lean,Kha/lean,soonhokong/lean-osx,soonhokong/lean-windows,avigad/lean,leanprover-community/lean,Kha/lean,johoelzl/lean,leanprover/lean,fpvandoorn/lean,johoelzl/lean,digama0/lean,leodemoura/lean,soonhokong/lean-windows,avigad/lean,soonhokong/lean-osx,leodemoura/lean,fpvandoorn/lean,soonhokong/lean-osx,rlewis1988/lean,Kha/lean,avigad/lean,rlewis1988/lean,dselsam/lean,leanprover-community/lean,fgdorais/lean,Kha/lean,rlewis1988/lean,leanprover/lean,fgdorais/lean,avigad/lean,leanprover/lean,fpvandoorn/lean,rlewis1988/lean