Merge pull request #875 from plotly/update-method

Introducing `Plotly.update`

Author: etpinard

Diff for: src/core.js

@@ -32,6 +32,7 @@ exports.newPlot = Plotly.newPlot;
 exports.restyle = Plotly.restyle;
 exports.relayout = Plotly.relayout;
 exports.redraw = Plotly.redraw;
+exports.update = Plotly.update;
 exports.extendTraces = Plotly.extendTraces;
 exports.prependTraces = Plotly.prependTraces;
 exports.addTraces = Plotly.addTraces;