v1.51.0

Added

• Add image trace type [#4289, #4307, #4313, #4319]
• Add automargin attribute in pie traces, enabling outside text labels
  to push the margins [#4278]
• Add title.standoff attribute to cartesian axes, setting the
  distance in pixels between the tick labels and the axis title [#4279]
• Add hoverongaps attribute to heatmap and contour traces,
  for suppressing hover labels on missing data [#4291]
• Add args2 attribute to updatemenus buttons which can be used to
  create toggle buttons [#4305]
• Add zh-CN locale [#4276, #4310]

Changed

• Introduce workarounds for "common" (aka axis) hover label clipping
  about the graph's viewport [#4298]
• No longer accept trace domain settings where end is not greater
  than start [#4304]

Fixed

• Fix streamtube coloring and positioning when generated
  with non-xyz grid signatures [#4271]
• Fix trace-type update calls on mapbox subplots [#4295]
• Fix width of box and violin items on log position axes [#4283]
• Fix box/meanline offset for one-sided vertical violin traces [#4314]
• Fix missing gaps in some scattergl line traces [#4316]
• Fix event data during scroll on gl3d subplots with orthographic projections [#4292]
• Handle data with identical positions in cone traces [#4306]
• Handle invalid entry before trying to render treemap trace [#4312]
• Fix heatmap and contour description for connectgaps [#4284]