title: liquibase diffchange log issue repeats the change set
body: <p>Hi I am facing one issue with diffChangelog.I have performed diffchangelog between two MSSQL databases I got list of change sets.I got following</p>
  
  <p>changeSet author="deekshith (generated)" id="1415884590690-1734"></p>
  
  <p>modifyDataType columnName="lingo_id" newDataType="char(36)" tableName="lingo"/></p>
  
  <p>addNotNullConstraint columnDataType="char(36)" columnName="lingo_id" tableName="lingo"/></p>
  
  <p>/changeSet</p>
  
  <p>I have update the change sets to respective database and again performed diffChangelog I got same as above again</p>
  
  <p>changeSet author="deekshith (generated)" id="1415884590690-1736"></p>
  
  <p>modifyDataType columnName="lingo_id" newDataType="char(36)" tableName="lingo"/></p>
  
  <p>addNotNullConstraint columnDataType="char(36)" columnName="lingo_id" tableName="lingo"/></p>
  
  <p>/changeSet</p>
  
  <p>Please let me know what I am doing wrong</p>