Force install of rebar on build

priv/build/build.sh

@@ -8,7 +8,8 @@ MIX_ENV=${MIX_ENV-prod}
 export MIX_ENV=$MIX_ENV
 
 # Clean project and get dependencies
-mix do local.hex --force, \
+mix do local.rebar --force, \
+       local.hex --force, \
        clean --only $MIX_ENV, \
        deps.get --only $MIX_ENV