Remove -y option when removing puby1.8

Since it is easily could break installations running on the server - hence the person doing the install should be able to make the decision to remove himself.

doc/install/installation.md

@@ -86,7 +86,7 @@ Then select 'Internet Site' and press enter to confirm the hostname.
 Remove the old Ruby 1.8 if present
-    sudo apt-get remove -y ruby1.8
+    sudo apt-get remove ruby1.8
 Download Ruby and compile it: