sequenceDiagram -> notetext css font is hardcoded

[agusmba]

See https://github.com/knsv/mermaid/blob/7c74107f360dee4bceb197a2802bfd89a2a8dc64/src/less/default/sequenceDiagram.less#L73

I think this is preventing me from modifying the font of notes.

I don't know if there is a good reason for this or could this be removed?

[tylerlong]

Please refer to mermaidjs/mermaid.cli#24 (comment)