rebar.config: bump meck version: 0.9.2 -> v1.2.0
This fixes a compilation error with recent Erlang/OTP 29:
[ 335s] ===> Compiling meck
[ 335s] ===> Compiling _checkouts/meck/src/meck_matcher.erl failed
[ 335s] meck_matcher.erl:76:6: 'catch ...' is deprecated; please use 'try ... catch ... end' instead.
[ 335s] Compile directive 'nowarn_deprecated_catch' can be used to suppress
[ 335s] warnings in selected modules.
Change-Id: If3409de1e09ac1b6ce3355d19e47ef0e160a2d3b
