Add new in mention

Author: LiamConnors

_posts/plotly_js/fundamentals/axes/2025-06-29-zeroline.html

@@ -6,6 +6,8 @@
 sitemap: false
 arrangement: horizontal
 markdown_content: |
+   *New in 3.1*
+   
    By default, zero lines are displayed below traces. Set `zerolinelayer="above traces"` on an axis to display its zero line above traces.
 ---
 var trace1 = {

_posts/plotly_js/fundamentals/hover/2025-07-29-unified-hover-template.html

@@ -6,6 +6,8 @@
 sitemap: false
 arrangement: horizontal
 markdown_content: |
+   *New in 3.1*
+   
    Customize the title shown in unified hovermode by specifying `unifiedhovertitle.text`. The unified hover title is a template string that supports using variables from the data. Numbers are formatted using d3-format's syntax `%{variable:d3-format}`, for example `"Price: %{y:$.2f}"`. Dates are formatted using d3-time-format's syntax `%{variable|d3-time-format}`, for example `"Day: %{x|%A}"`.
 ---
 var data = [