Make the --solve_constraints flag description a bit clearer

Author: xxdavid

src/gradualizer_cli.erl

@@ -100,7 +100,7 @@ print_usage() ->
     io:format("       --no_fancy                - Don't use fancy error messages.~n"),
     io:format("       --union_size_limit        - Performance hack: Unions larger than this value~n"),
     io:format("                                   are replaced by any() in normalization (default: 30)~n"),
-    io:format("       --solve_constraints       - Use the experimental constraint solver (off by default)~n").
+    io:format("       --solve_constraints       - Type check polymorphic calls (off by default)~n").
 
 -spec parse_opts([string()], gradualizer:options()) -> {[string()], gradualizer:options()}.
 parse_opts([], Opts) ->