v1.1.1

• When using SQL schema dump in MySQL, don't output the generation date in order
  to have the same output if nothing changed. (Joseph Halter)
• Fix readme formatting (Ben Koshy)
  #175
• Add frozen_string_literal to migration template (Semyon Pupkov)
  #174
• Add allow_missing_migration_files option (Semyon Pupkov)
  #172
  #173