[defns.referenceable] Remove duplicate 'an'

Author: tkoeppe

source/lib-intro.tex

@@ -293,7 +293,7 @@
 \definition{referenceable type}{defns.referenceable}
 \indexdefn{type!referenceable}%
 type that is either an
-an object type, a function type that does not have cv-qualifiers or a
+object type, a function type that does not have cv-qualifiers or a
 \grammarterm{ref-qualifier}, or a reference type
 
 \begin{defnote}