Bump base upper bound to 4.15

directory.cabal

@@ -55,7 +55,7 @@ Library
     include-dirs: .
 
     build-depends:
-        base     >= 4.5 && < 4.14,
+        base     >= 4.5 && < 4.15,
         time     >= 1.4 && < 1.10,
         filepath >= 1.3 && < 1.5
     if os(windows)