Bug#929426: acorn build-depends on cruft package node-unicode-11.0.0

[Peter Michael Green]

package: acorn
version: 5.5.3+ds3-2
severity: serious
acorn build-depends on node-unicode-11.0.0 which is no longer built by 
source package node-unicode-data. It appears to have been replaced by 
node-unicode-12.0.0