tundra: Use language-specific heredocs

Author: issyl0

Formula/t/tundra.rb

@@ -53,7 +53,7 @@ def install
       ["linux", "gcc"]
     end
 
-    (testpath/"tundra.lua").write <<~EOS
+    (testpath/"tundra.lua").write <<~LUA
       Build {
         Units = function()
           local test = Program {
@@ -70,7 +70,7 @@ def install
           },
         },
       }
-    EOS
+    LUA
     system bin/"tundra2"
     system "./t2-output/#{os}-#{cc}-debug-default/test"
   end