loosen base constraints

we need ghc 8.6.5 compatibility which means base 4.12

gbs-downloader.cabal

-cabal-version:   3.0
+cabal-version:   2.4
 
 -- The cabal-version field refers to the version of the .cabal specification,
 -- and can be different from the cabal-install (the tool) version and the
@@ -88,7 +88,7 @@ library
   -- Other library packages from which modules are imported.
   build-depends:
     , aeson
-    , base                     ^>=4.14.3.0
+    , base
     , base32
     , base64
     , binary
@@ -130,7 +130,7 @@ executable gbs-download
   -- Other library packages from which modules are imported.
   build-depends:
     , aeson
-    , base            ^>=4.14.3.0
+    , base
     , bytestring
     , containers
     , gbs-downloader
@@ -168,7 +168,7 @@ test-suite gbs-downloader-test
 
   -- Test dependencies.
   build-depends:
-    , base            ^>=4.14.3.0
+    , base
     , base32
     , binary
     , bytestring