GUACAMOLE-1491: Merge fix environment name of GUACD_PORT

diff --git a/src/guacamole-docker.md b/src/guacamole-docker.md
index 30b9db3..a4ce1a4 100644
--- a/src/guacamole-docker.md
+++ b/src/guacamole-docker.md
@@ -146,7 +146,7 @@
 : The hostname of the guacd instance to use to establish remote desktop
   connections. *This is required if you are not using Docker to provide guacd.*
 
-`GUACD_POST`
+`GUACD_PORT`
 : The port that Guacamole should use when connecting to guacd. This environment
   variable is optional. If not provided, the standard guacd port of 4822 will
   be used.