Fix caching to prevent displaying the wrong variant

[mhkc]

This PR fixes a bug that could cause the wrong to be displayed different regions were being displayed for the same case at the same time.

close #133

How to test:

1. Use example variant in production Gens, http://cmdscout2.lund.skane.se/gens/24MD00143?region=6:32002301-32016300&variant=ee7d5522e87b70eb5bf525a6fce18104&genome_build=38&case_id=24MD00143&individual_id=24MD00143
2. Try repoducing the bug by first opening the variant in the production version of Gens.
3. Then change chromosome 6 to 8 in the url just after the page has loaded
4. Verify that the chromosome number has not changed to 8 and the variant is still being displayed.
5. Open the same variant in the dev version of Gens by replacing gens with gens_dev in the URL and repeat the steps above to reproduce the bug,

Expected outcome:
The new region and variant should be displayed.

Review:

• code approved by

[alkc]

The test checks out. Changing the chromosome in the url in gens_dev loads the correct chromosome position. This does not occur on the production instance.

[alkc]

I've reran the tests and can confirm the bug is fixed in the dev instance.