Use packageAt:ifAbsent: in chunk exporter.

#packageAt: is deprecated.

src/Wrappers-JQuery.st

@@ -1,5 +1,5 @@
 Smalltalk createPackage: 'Wrappers-JQuery'!
-(Smalltalk packageAt: 'Wrappers-JQuery') imports: {'jQuery' -> 'jquery'}!
+(Smalltalk packageAt: 'Wrappers-JQuery' ifAbsent: [ self error: 'Package not created: Wrappers-JQuery' ]) imports: {'jQuery' -> 'jquery'}!
 Object subclass: #JQuery
 	instanceVariableNames: ''
 	package: 'Wrappers-JQuery'!