Corrected spelling
Corrected spelling

Changed "singing" to "signing."

 This closes #661

stevengill/cordova-docs,tony--/cordova-docs,purplecabbage/cordova-docs,apache/cordova-docs,purplecabbage/cordova-docs,stevengill/cordova-docs,tony--/cordova-docs,tony--/cordova-docs,purplecabbage/cordova-docs,apache/cordova-docs,shazron/cordova-docs,stevengill/cordova-docs,purplecabbage/cordova-docs,shazron/cordova-docs,shazron/cordova-docs,apache/cordova-docs,shazron/cordova-docs,stevengill/cordova-docs,apache/cordova-docs