Fix typo in core/server/master/src/main/java/alluxio/master/file/activesync/ActiveSyncManager.java

[apc999]

In https://github.com/Alluxio/alluxio/blob/8f74e6584b6d2d71be3a3737057808b6f77c44ae/core/server/master/src/main/java/alluxio/master/file/activesync/ActiveSyncManager.java#L105

Fix "Constructs a Active Sync Manager" to be "Constructs an Active Sync Manager"

[jojodaser]

/assign @jojodaser

[brondou666]

/assign @brondou666