Fix to readthedocs builds

.readthedocs.yml

@@ -3,5 +3,4 @@ formats: all
 python:
   version: 3
   install:
-    - requirements: doc/requirements.txt
-  system_packages: true
+    - requirements: doc/requirements.txt

CHANGELOG.md

@@ -4,6 +4,7 @@ _**Version 1.5.1:**_
 
 **Bug fixes**
 
+- Fix to readthedocs building after system packages no longer imported [#336](https://github.com/tobac-project/tobac/pull/336)
 - The `strict_thresholding` option in feature detection now works correctly for detecting minima, and produces the same results as without strict thresholding if the `n_min_threshold` is a scalar value [#316](https://github.com/tobac-project/tobac/pull/316)
 
 
@@ -42,13 +43,16 @@ _**Version 1.5.0:**_
 - `scipy.interpolate.interp2d` in `add_coordinates` and `add_coordinates_3D` has been replaced with `scipy.interpolate.interpn` as `interp2d` has been deprecated. [#279](https://github.com/tobac-project/tobac/pull/279) 
 - `setup.py` updated to draw its required packages from `requirements.txt` [#288](https://github.com/tobac-project/tobac/pull/288)
 
+
+
 **Repository Enhancements**
 
 - New CI was added to automatically check the example and documentation Jupyter notebooks [#258](https://github.com/tobac-project/tobac/pull/258), [#290](https://github.com/tobac-project/tobac/pull/290)
 - The `check_formatting` CI action has been revised to install dependencies through `conda` [#288](https://github.com/tobac-project/tobac/pull/288)
 - Repository authors updated [#289](https://github.com/tobac-project/tobac/pull/289)
 - CI added to check author list formatting for Zenodo [#292](https://github.com/tobac-project/tobac/pull/292)
 
+
 **Deprecations**
 
 - All functions in `centerofgravity.py` (`calculate_cog`, `calculate_cog_untracked`, `center_of_gravity`) have been deprecated and will be removed or significantly changed in v2.0. [#200](https://github.com/tobac-project/tobac/pull/200)
@@ -58,8 +62,10 @@ _**Version 1.5.0:**_
 - `tobac.utils.combine_tobac_feats` has been renamed to `tobac.utils.combine_feature_dataframes`, and the original name has been deprecated and will be removed in a future release. [#300](https://github.com/tobac-project/tobac/pull/300)
 
 
+
 _**Version 1.4.2:**_
 
+
 **Bug fix**
 
 - Fixed a bug in the segmentation procedure that assigned the wrong grid cell areas to features in data frame  [#246](https://github.com/tobac-project/tobac/pull/246)
@@ -80,7 +86,6 @@ _**Version 1.4.1:**_
 
 - Regenerated example notebooks so that they are up to date for the present version [#233](https://github.com/tobac-project/tobac/pull/233)
 
-
 _**Version 1.4.0:**_
 
 **Enhancements**
@@ -118,14 +123,12 @@ _**Version 1.4.0:**_
 
 - Support for Python 3.6 and earlier is now deprecated and will be removed in v1.5.0 ([#193](https://github.com/tobac-project/tobac/pull/193))
 
-
 _**Version 1.3.3:**_
 
 **Bug fixes**
 
 - Added a workaround to a bug in trackpy that fixes predictive tracking [#170](https://github.com/tobac-project/tobac/pull/170)
 
-
 _**Version 1.3.2:**_
 
 **Bug fixes**
@@ -138,7 +141,6 @@ _**Version 1.3.2:**_
 - Added automatic code coverage reports [#124](https://github.com/tobac-project/tobac/pull/124)
 - Added automatic building of readthedocs documentation on pull requests
 
-
 _**Version 1.3.1:**_
 
 **Enhancements**
@@ -153,7 +155,6 @@ _**Version 1.3.1:**_
 
 - New pull request template for the repository, including a checklist to be completed for each pull request [#120](https://github.com/tobac-project/tobac/pull/120)
 
-
 _**Version 1.3:**_
 
 **Enhancements**