message: Minor change to migration guide.
diff: ## Migrating from 0.2.* to 0.3.*
  Criterion.rs took advantage of 0.3.0 being a breaking-change release to make a number of changes
  -that will require changes to user code.
  +that will require changes to user code. These changes are documented here, along with the newer
  +alternatives.
  ### `Benchmark`, `ParameterizedBenchmark`, `Criterion::bench_functions`, `Criterion::bench_function_over_inputs`, `Criterion::bench` are deprecated.
  