Fix typo

Author: dzampino

README

@@ -2,5 +2,5 @@ As of Nov 1st 2016, active development on "Windows for OpenSSH" is being done in
 
 This repo (https://github.com/PowerShell/Win32-OpenSSH) is being maintained to keep track of releases and issues.
 
-Release Histroy:
+Release History:
 7/26/2018 -- Release 7.7.2.0 with source https://github.com/PowerShell/openssh-portable/releases/tag/v7.7.2.0