update to newest mermaid to get subgraphs and gantt

[timelyportfolio]

This pull will update to the newest version of mermaid. Some changes should be noted

1. Styling changes as mermaid uses a blend of old styling behavior with some new css defined in mermaid.css
2. Subgraphs now supported
3. Preliminary support for Gantt charts

I'll post some examples below. Tests of previous behavior and functionality using examples in Readme.md and other documentation all seemed to work, but please verify on your side.

Subgraph Example

This example comes from the mermaid documentation.

library(DiagrammeR)

mermaid('
graph TB
         subgraph one
         a1-->a2
         end
         subgraph two
         b1-->b2
         end
         subgraph three
         c1-->c2
         end
         c1-->a2
')

Gantt Chart example

This example comes from the mermaid documentation for Gantt.

library(DiagrammeR)
mermaid('
       gantt
        dateFormat  YYYY-MM-DD
        title Adding GANTT diagram functionality to mermaid

        section A section
        Completed task            :done,    des1, 2014-01-06,2014-01-08
        Active task               :active,  des2, 2014-01-09, 3d
        Future task               :         des3, after des2, 5d
        Future task2               :         des4, after des3, 5d

        section Critical tasks
        Completed task in the critical line :crit, done, 2014-01-06,24h
        Implement parser and jison          :crit, done, after des1, 2d
        Create tests for parser             :crit, active, 3d
        Future task in critical line        :crit, 5d
        Create tests for renderer           :2d
        Add to mermaid                      :1d

        section Documentation
        Describe gantt syntax               :active, a1, after des1, 3d
        Add gantt diagram to demo page      :after a1  , 20h
        Add another diagram to demo page    :doc1, after a1  , 48h

        section Last section
        Describe gantt syntax               :after doc1, 3d
        Add gantt diagram to demo page      : 20h
        Add another diagram to demo page    : 48h
')