Fix environment variable name in man-page (#1806)

doc/yay.8

@@ -140,7 +140,7 @@ Prints the PKGBUILD of the given packages to stdout.
 
 .TP
 Web related operations such as voting for AUR packages.
-Requires setting AUR_USER and AUR_PASSWORD environment variables.
+Requires setting AUR_USERNAME and AUR_PASSWORD environment variables.
 
 .TP
 .B \-u, \-\-unvote