fix(docs): correct PR number

Signed-off-by: F.N. Claessen <felix@seita.nl>

documentation/changelog.rst

@@ -11,7 +11,7 @@ New features
 
 * Introduce new reporter to compute profit/loss due to electricity flows: `ProfitOrLossReporter` [see `PR #808 <https://github.com/FlexMeasures/flexmeasures/pull/808>`_ and `PR #844 <https://github.com/FlexMeasures/flexmeasures/pull/844>`_]
 * Charts visible in the UI can be exported to PNG or SVG formats in a more automated fashion, using the new CLI command flexmeasures show chart [see `PR #833 <https://github.com/FlexMeasures/flexmeasures/pull/833>`_]
-* Sensor charts showing instantaneous observations can be interpolated by setting the ``interpolate`` sensor attribute to one of the `supported Vega-Lite interpolation methods <https://vega.github.io/vega-lite/docs/area.html#properties>`_ [see `PR #850 <https://github.com/FlexMeasures/flexmeasures/pull/850>`_]
+* Sensor charts showing instantaneous observations can be interpolated by setting the ``interpolate`` sensor attribute to one of the `supported Vega-Lite interpolation methods <https://vega.github.io/vega-lite/docs/area.html#properties>`_ [see `PR #851 <https://github.com/FlexMeasures/flexmeasures/pull/851>`_]
 
 Infrastructure / Support
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