v0.8.15

WebIO v0.8.15

Diff since v0.8.14

Closed issues:

• 'webio_serve not defined' when Mux loaded (#420)
• MethodError: no method matching eachcolumn, on basic example (#421)
• WebIO (#431)

Merged pull requests:

• Change internal bookkeeping for Observables and Scopes (#410) (@travigd)
• Fixed @get! deprecation warning (#428) (@rasmushenningsson)
• Support for JupyterLab 2.x (closes #397) (#430) (@lcontento)