doc: Fix typo

From: Alexander Law <exclusion@gmail.com>

doc/src/sgml/gin.sgml

@@ -179,7 +179,7 @@
        <function>extractQuery</> to pass additional data to the
        <function>consistent</> and <function>comparePartial</> methods.
        To use it, <function>extractQuery</> must allocate
-       an array of <literal>*nkeys</> Pointers and store its address at
+       an array of <literal>*nkeys</> pointers and store its address at
        <literal>*extra_data</>, then store whatever it wants to into the
        individual pointers.  The variable is initialized to NULL before
        call, so this argument can simply be ignored by operator classes that