[sledge] Do not set -error-style short

Summary:
Remove `-error-style short` from the compilation flags since it causes
merlin to complain, see https://github.com/ocaml/merlin/issues/1176.
After this diff, developers will need to set `OCAML_ERROR_STYLE=short`
in their environment.

Reviewed By: jvillard

Differential Revision: D24306066

fbshipit-source-id: 9c4f26393

sledge/dune

@@ -7,7 +7,7 @@
  (debug
   (flags
    (-w +a-4-9-18-30-40-42-44-48@50-66 -strict-formats -strict-sequence
-     -error-style short -short-paths -bin-annot -keep-locs -keep-docs -opaque))
+     -short-paths -bin-annot -keep-locs -keep-docs -opaque))
   (env-vars
    (PPX_TRACE_ENABLED 1))
   (inline_tests enabled))