The easiest way to find out is to use 7-Zip to open up the MSI file, expand media1.cab file, and extract the file "Microsoft_Azure_ActiveDirectory_Synchronization_Setup_dll".
Rename it to "Microsoft_Azure_ActiveDirectory_Synchronization_Setup_dll.dll" and right click on the file, Properties and then Details tab:
In my case, it's version 1.0.9131, released in December 2015.
You can get the full version history for Azure AD Connect here:
Bonus tip! To manually force a sync using AADConnect 1.1, run the following PowerShell cmdlets:
Start-ADSyncSyncCycle -PolicyType Initial
Start-ADSyncSyncCycle -PolicyType Delta