Add v1hovermode to the list of all the modebar options

fixes plotly#3274

The list often serves as reference to look for modebar options and v1hovermode was missing.

Author: JulianWgs

Diff for: doc/python/configuration-options.md

@@ -207,7 +207,7 @@ fig.show(config=config)
 To delete buttons from the modebar, pass an array of strings containing the names of the buttons you want to remove to the `modeBarButtonsToRemove` attribute in the figure's configuration dictionary. Note that different chart types have different default modebars. The following is a list of all the modebar buttons and the chart types they are associated with:
 
   - **High-level**: `zoom`, `pan`, `select`, `zoomIn`, `zoomOut`, `autoScale`, `resetScale`
-  - **2D**: `zoom2d`, `pan2d`, `select2d`, `lasso2d`, `zoomIn2d`, `zoomOut2d`, `autoScale2d`, `resetScale2d`
+  - **2D**: `zoom2d`, `pan2d`, `select2d`, `lasso2d`, `zoomIn2d`, `zoomOut2d`, `autoScale2d`, `resetScale2d`, `v1hovermode`
   - **2D Shape Drawing**: `drawline`, `drawopenpath`, `drawclosedpath`, `drawcircle`, `drawrect`, `eraseshape`
   - **3D**: `zoom3d`, `pan3d`, `orbitRotation`, `tableRotation`, `handleDrag3d`, `resetCameraDefault3d`, `resetCameraLastSave3d`, `hoverClosest3d`
   - **Cartesian**: `hoverClosestCartesian`, `hoverCompareCartesian`