fix: Fixed typo in upgrade guide (#1321)

see also http://www.dictionary.com/browse/per-say

Author: mwittig

UPGRADE_GUIDE.md

@@ -2,7 +2,7 @@ Upgrading from 5.x to 6.x
 -------------
 TLDR: You probably don't have to change anything. You might need to enable `rtscts` in your open options.
 
-* **binaries:** I'm considering the switch to `prebuild` a breaking change because it's substantially changes our install processes. It's also possible the install flags to ensure downloading or building from source has changed slightly. That's not our api per say, but it's enough.
+* **binaries:** I'm considering the switch to `prebuild` a breaking change because it's substantially changes our install processes. It's also possible the install flags to ensure downloading or building from source has changed slightly. That's not our api per se, but it's enough.
 * **windows:** We previously hard coded to have RTS on for windows at all times it now default to off.