dhall-lsp-server: Fix lower bound on dhall (#1495)

* dhall-lsp-server: Fix lower bound on dhall

… as reported in #1494.

* Require base >= 4.11

Previously there were build failures with GHC-8.2 and 8.0 due to `(<>)` being out of scope.

Author: sjakobi

dhall-lsp-server/dhall-lsp-server.cabal

@@ -45,12 +45,12 @@ library
   build-depends:
       aeson                >= 1.3.1.1  && < 1.5
     , aeson-pretty         >= 0.8.7    && < 0.9
-    , base                 >= 4.7      && < 5
+    , base                 >= 4.11     && < 5
     , bytestring           >= 0.10.8.2 && < 0.11
     , containers           >= 0.5.11.0 && < 0.7
     , data-default         >= 0.7.1.1  && < 0.8
     , directory            >= 1.2.2.0  && < 1.4
-    , dhall                >= 1.26.0   && < 1.28
+    , dhall                >= 1.27.0   && < 1.28
     , dhall-json           >= 1.4      && < 1.6
     , filepath             >= 1.4.2    && < 1.5
     , haskell-lsp          >= 0.15.0.0 && < 0.17