fix(lib/ace/mode/lean_highlight_rules.js): highlight for definition name
fix(lib/ace/mode/lean_highlight_rules.js): highlight for definition name

close #83

leanprover/ace,leanprover/ace,leanprover/ace,leanprover/ace,leanprover/ace,leanprover/ace,leanprover/ace,leanprover/ace,leanprover/ace,leanprover/ace,leanprover/ace,leanprover/ace,leanprover/ace,leanprover/ace,leanprover/ace,leanprover/ace,leanprover/ace,leanprover/ace