Add transformers-compat for ancients MTL/Transformer versions

.gitignore

@@ -1,4 +1,4 @@
-*.sw[pon]
+*.sw[ponmkl]
 .stack-work
 dist
 .cabal-sandbox

protolude.cabal

@@ -64,19 +64,20 @@ library
     -fwarn-implicit-prelude
 
   build-depends:       
-    base             >= 4.6  && <4.11,
-    array            >= 0.4  && <0.6,
-    ghc-prim         >= 0.3  && <0.6,
-    async            >= 2.0  && <2.2,
-    deepseq          >= 1.3  && <1.5,
-    containers       >= 0.5  && <0.6,
-    hashable         >= 1.2  && <1.3,
-    transformers     >= 0.2  && <0.6,
-    text             >= 1.2  && <1.3,
-    stm              >= 2.4  && <2.5,
-    bytestring       >= 0.10 && <0.11,
-    mtl              >= 2.1  && <2.3,
-    mtl-compat       >= 0.2  && <0.3
+    base                >= 4.6  && <4.11,
+    array               >= 0.4  && <0.6,
+    ghc-prim            >= 0.3  && <0.6,
+    async               >= 2.0  && <2.2,
+    deepseq             >= 1.3  && <1.5,
+    containers          >= 0.5  && <0.6,
+    hashable            >= 1.2  && <1.3,
+    transformers        >= 0.2  && <0.6,
+    text                >= 1.2  && <1.3,
+    stm                 >= 2.4  && <2.5,
+    bytestring          >= 0.10 && <0.11,
+    mtl                 >= 2.1  && <2.3,
+    mtl-compat          >= 0.2  && <0.3,
+    transformers-compat >= 0.4  && <0.6
 
   if impl(ghc >= 7.8.0)
     build-depends: