Update drf-haystack to 1.9.1

Author: jmroot

app/requirements.txt

@@ -24,7 +24,7 @@ django-notifications-hq==1.8.3
 django-recaptcha==4.1.0
 djangorestframework==3.15.2
 docutils==0.16
-drf-haystack==1.8.13
+drf-haystack==1.9.1
 elasticsearch==7.8.1
 filelock==3.19.1
 gprof2dot==2019.11.30