Fix monoid instance for ShapeBinding.
Fix monoid instance for ShapeBinding.

ihc/futhark,diku-dk/futhark,HIPERFIT/futhark,diku-dk/futhark,CulpaBS/wbBach,diku-dk/futhark,mrakgr/futhark,diku-dk/futhark,mrakgr/futhark,HIPERFIT/futhark,ihc/futhark,mrakgr/futhark,diku-dk/futhark,HIPERFIT/futhark,ihc/futhark