message: docs(compat): fix typo in readme
  fix typo in readme referring to previous (pervious) RxJS versions
diff: # RxJS Compatibility Package
  -This package is required to get backwards compatibility with RxJS pervious to version 6. It contains the imports to add operators to `Observable.prototype` and creation methods to `Observable`. This is what allows, for instance, dot-chaining:
  +This package is required to get backwards compatibility with RxJS previous to version 6. It contains the imports to add operators to `Observable.prototype` and creation methods to `Observable`. This is what allows, for instance, dot-chaining:
  ```
  Observable.interval(1)
  