FIx typo in pldoc for require_prolog_versoin/2

Author: jamesnvc

library/prolog_versions.pl

@@ -84,8 +84,8 @@
 %     - warning(Feature)
 %       Only print a warning instead of throwing an error.
 %     - library(Lib)
-%       Demand library(Lib) to be present.  Thde library not being
-%       there may indicate an incomplete installation.  For example
+%       Demand library(Lib) to be present.  The library not being
+%       there may indicate an incomplete installation.  For example,
 %       library(pce) to demand xpce graphics support.
 %     - Flag
 %       Demand current_prolog_flag(Flag, true) to be true.