[ML][DOCS] Fix bucket_span type in results resources (elastic/x-pack-elasticsearch#2714)
[ML][DOCS] Fix bucket_span type in results resources (elastic/x-pack-elasticsearch#2714)

Original commit: elastic/x-pack-elasticsearch@af24bde71ff885d25809498343347f0accb2627f

coding0011/elasticsearch,uschindler/elasticsearch,coding0011/elasticsearch,GlenRSmith/elasticsearch,uschindler/elasticsearch,gingerwizard/elasticsearch,gingerwizard/elasticsearch,gingerwizard/elasticsearch,nknize/elasticsearch,gingerwizard/elasticsearch,gingerwizard/elasticsearch,gfyoung/elasticsearch,HonzaKral/elasticsearch,robin13/elasticsearch,nknize/elasticsearch,coding0011/elasticsearch,nknize/elasticsearch,coding0011/elasticsearch,scorpionvicky/elasticsearch,gingerwizard/elasticsearch,GlenRSmith/elasticsearch,nknize/elasticsearch,uschindler/elasticsearch,uschindler/elasticsearch,gfyoung/elasticsearch,coding0011/elasticsearch,scorpionvicky/elasticsearch,robin13/elasticsearch,GlenRSmith/elasticsearch,GlenRSmith/elasticsearch,scorpionvicky/elasticsearch,robin13/elasticsearch,scorpionvicky/elasticsearch,gfyoung/elasticsearch,robin13/elasticsearch,GlenRSmith/elasticsearch,uschindler/elasticsearch,HonzaKral/elasticsearch,nknize/elasticsearch,HonzaKral/elasticsearch,robin13/elasticsearch,scorpionvicky/elasticsearch,HonzaKral/elasticsearch,gingerwizard/elasticsearch,gfyoung/elasticsearch,gfyoung/elasticsearch