English grammar: Fix incorrect use of word "deprecated" (#855)

Sorry for the grammar nit-picking, but by the following definition, these options are **already** deprecated.

> deprecated. Adjective. (computing) Obsolescent; said of a construct in a computing language considered old, and planned to be phased out, but still available for use.
> https://en.wiktionary.org/wiki/deprecated

lib/mysql2/client.rb

@@ -66,7 +66,7 @@ def initialize(opts = {})
 
       if [:user, :pass, :hostname, :dbname, :db, :sock].any? { |k| @query_options.key?(k) }
         warn "============= WARNING FROM mysql2 ============="
-        warn "The options :user, :pass, :hostname, :dbname, :db, and :sock will be deprecated at some point in the future."
+        warn "The options :user, :pass, :hostname, :dbname, :db, and :sock are deprecated and will be removed at some point in the future."
         warn "Instead, please use :username, :password, :host, :port, :database, :socket, :flags for the options."
         warn "============= END WARNING FROM mysql2 ========="
       end