use 0.6.0-pre as minimum julia version (#256)

tkelman · ararslan · commit c27e3565b6b0 · 2017-05-25T13:49:29.000-07:00
since struct syntax wouldn't work on early 0.6.0-dev versions,
better to stick with the julia-0.5-compatible versions of the package there
diff --git a/REQUIRE b/REQUIRE
@@ -1,4 +1,4 @@
-julia 0.6-
+julia 0.6.0-pre
 Compat 0.8.6
 StatsBase 0.14.0
 Reexport
