Using integer type in job spec configs causes panic

[kushsharma]

Currently, job spec yaml configuration only supports string key-value pairs. Having string kv pairs are fine but passing int(or any other type) should handle the failure gracefully instead of panic.

panic: interface conversion: interface {} is int, not string
goroutine 1 [running]:
github.com/odpf/optimus/store/local.JobSpecAdapter.ToSpec
....