Add .l to Groff.

lib/linguist/heuristics.rb

@@ -290,11 +290,13 @@ module Linguist
       end
     end
 
-    disambiguate "Common Lisp", "Lex" do |data|
+    disambiguate "Common Lisp", "Lex", "Groff" do |data|
       if data.include?("(def(un|macro)\s")
         Language["Common Lisp"]
       elsif /^(%[%{}]xs|<.*>)/.match(data)
         Language["Lex"]
+      elsif /^\.[a-z][a-z](\s|$)/.match(data)
+        Language["Groff"]
       end
     end
   end

lib/linguist/languages.yml

@@ -1214,6 +1214,7 @@ Groff:
   - '.5'
   - '.6'
   - '.7'
+  - .l
   tm_scope: text.groff
   aliases:
   - nroff