fix typo in Fixes section of learn
"* [`Data Preparation Methods`](https://developers.arcgis.com/python/api-reference/arcgis.learn.toc.html#data-preparation-methods)\n",
" * Fixes `expected scalar type Float` Exception with [`prepare_data()`](https://developers.arcgis.com/python/api-reference/arcgis.learn.toc.html#prepare-data) when using `pytorch 1.7.0`\n",
"* [`Pixel Classification Models`](https://developers.arcgis.com/python/api-reference/arcgis.learn.toc.html#pixel-classification-models)\n",
- " * Fixes `fit()` method in segmentation models not returning `NaN` values for certain attributes: [`UNetClassifier`](https://developers.arcgis.com/python/api-reference/arcgis.learn.toc.html#unetclassifier), [`PSPNetClassifier`](https://developers.arcgis.com/python/api-reference/arcgis.learn.toc.html#pspnetclassifier), [`DeepLab`](https://developers.arcgis.com/python/api-reference/arcgis.learn.toc.html#deeplab)\n",
+ " * Fixes `fit()` method in segmentation models returning `NaN` values for certain attributes: [`UNetClassifier`](https://developers.arcgis.com/python/api-reference/arcgis.learn.toc.html#unetclassifier), [`PSPNetClassifier`](https://developers.arcgis.com/python/api-reference/arcgis.learn.toc.html#pspnetclassifier), [`DeepLab`](https://developers.arcgis.com/python/api-reference/arcgis.learn.toc.html#deeplab)\n",
" * [`MultiTaskRoadExtractor`](https://developers.arcgis.com/python/api-reference/arcgis.learn.toc.html?highlight=retinanet#multitaskroadextractor) \n",
" * Fixes issue for [`show_results()`](https://developers.arcgis.com/python/api-reference/arcgis.learn.toc.html?highlight=retinanet#arcgis.learn.MultiTaskRoadExtractor.show_results) plotting images incorrectly\n",
" * Fixes issue causing [`save()`](https://developers.arcgis.com/python/api-reference/arcgis.learn.toc.html?highlight=retinanet#arcgis.learn.MultiTaskRoadExtractor.save) only to work after calling [`fit()`](https://developers.arcgis.com/python/api-reference/arcgis.learn.toc.html?highlight=retinanet#arcgis.learn.MultiTaskRoadExtractor.save)\n",
