v3.2.0

[jheer]

Changes:

• Add pivot transform. (Pivot transform (feature request) vega-transforms#5)
• Fix scale lookup for gradient expr function. (gradient() expression func throws an error on scale name #1143)
• Add target loader option for setting browser target attribute for sanitized hyperlinks. (Specify target in href links #1171)
• Fix View initialization to ensure scenegraph handler receives correct loader instance. (Specify target in href links #1171)
• Fix implicit ordinal scale construction with explicit domain. (Invalid scale reference causes domain pollution (for multi-field data ref domain) #1166)
• Fix JSON schema for data source and fontWeight channel.
• Export TypeScript typings.
• Update documentation.