Update rebar/enc binaries to R15B03-1

The recent release of Erlang 23.0 removed support for loading beam
modules compiled under R14 and earlier. Thus we're now forced to abandon
support for R13 and R14.

.gitignore

@@ -1,5 +1,6 @@
 .eunit
 .rebar
+.tool-versions
 .jiffy.dev
 *.app
 *.beam