Overall, there isn't that much movement in Steam's report. Everything other than Windows 10 64-Bit reportedly decreased in share, but they're all within margin of error, the same is the case with both Mac OS and Linux.
However, one number does stick out in particular. Windows 10 overall has reached its highest point, but only by a fraction. In April, it held a share at its highest point of 51.20%, but has decreased since then. Now, in June, Windows 10 has reached 51.23% share, a new high.
It is important to remember that Steam's survey is based on users who have opted-in to the survey, and have been active during that month. This means it is by no means a look at the true configurations of Steam's users.