docs: fix typo in query function example in Plugin Writer's Guide
docs: fix typo in query function example in Plugin Writer's Guide

https://bugzilla.gnome.org/show_bug.cgi?id=696142

justinjoy/gstreamer,shelsonjava/gstreamer,jpxiong/gstreamer,Lachann/gstreamer,krieger-od/gstreamer,krichter722/gstreamer,lubosz/gstreamer,lovebug356/gstreamer,lovebug356/gstreamer,krieger-od/gstreamer,jpakkane/gstreamer,krieger-od/gstreamer,lubosz/gstreamer,krichter722/gstreamer,StreamUtils/gstreamer,centricular/gstreamer,Lachann/gstreamer,collects/gstreamer,mparis/gstreamer,cablelabs/gstreamer,surround-io/gstreamer,surround-io/gstreamer,ensonic/gstreamer,surround-io/gstreamer,mparis/gstreamer,cfoch/gstreamer,shelsonjava/gstreamer,mparis/gstreamer,cfoch/gstreamer,jpxiong/gstreamer,surround-io/gstreamer,lovebug356/gstreamer,centricular/gstreamer,StreamUtils/gstreamer,shelsonjava/gstreamer,lubosz/gstreamer,collects/gstreamer,jpakkane/gstreamer,ensonic/gstreamer,krichter722/gstreamer,StreamUtils/gstreamer,cablelabs/gstreamer,jpakkane/gstreamer,collects/gstreamer,shelsonjava/gstreamer,Lachann/gstreamer,cfoch/gstreamer,jpxiong/gstreamer,jpakkane/gstreamer,jpakkane/gstreamer,ensonic/gstreamer,lovebug356/gstreamer,mparis/gstreamer,centricular/gstreamer,centricular/gstreamer,justinjoy/gstreamer,krieger-od/gstreamer,justinjoy/gstreamer,cablelabs/gstreamer,justinjoy/gstreamer,lubosz/gstreamer,Lachann/gstreamer,krichter722/gstreamer,jpxiong/gstreamer,lovebug356/gstreamer,StreamUtils/gstreamer,collects/gstreamer,ensonic/gstreamer,jpxiong/gstreamer,shelsonjava/gstreamer,lubosz/gstreamer,cablelabs/gstreamer,cablelabs/gstreamer,mparis/gstreamer,krichter722/gstreamer,collects/gstreamer,centricular/gstreamer,surround-io/gstreamer,cfoch/gstreamer,krieger-od/gstreamer,StreamUtils/gstreamer,justinjoy/gstreamer,ensonic/gstreamer,cfoch/gstreamer,Lachann/gstreamer