Fix indentation in changeLog.xml example

[JohnScience]

In https://neo4j.com/labs/liquibase/docs/quickstart/#__tabbed_1_4,

databaseChangeLog:
- changeSet:
  id: my-movie-init
  author: fbiville
  changes:
  - cypher: 'CREATE (:Movie {title: ''My Life'', genre: ''Comedy''})'

the indentation is off, which causes changeSet: to be parsed as a null.

Other code examples, e.g. https://neo4j.com/labs/liquibase/docs/reference-features/#__tabbed_1_3

databaseChangeLog:
  - changeSet:
      id: my-movie-init
      author: fbiville
      changes:
        - cypher: 'CREATE (:Movie {title: ''My Life'', genre: ''Comedy''})'
  - changeSet:
      id: translate
      author: fbiville
      changes:
        - cypher: 'MATCH (m:Movie {title: ''My Life''}) SET m.genre = ''Comédie'''
      rollback:
        - cypher: 'MATCH (m:Movie {title: ''My Life''}) SET m.genre = ''Comedy'''

demonstrate proper indentation.