CI: fix missing version updates from 7.x to 7.10

Author: swallez

.jenkins/test-matrix.yml

@@ -1,7 +1,7 @@
 ---
 
 STACK_VERSION:
-  - 7.x-SNAPSHOT
+  - 7.10-SNAPSHOT
 
 GO_VERSION:
   - 1-alpine

Makefile

@@ -247,7 +247,7 @@ godoc: ## Display documentation for the package
 	godoc --http=localhost:6060 --play
 
 cluster: ## Launch an Elasticsearch cluster with Docker
-	$(eval version ?= "elasticsearch-oss:7.x-SNAPSHOT")
+	$(eval version ?= "elasticsearch-oss:7.10-SNAPSHOT")
 ifeq ($(origin nodes), undefined)
 	$(eval nodes = 1)
 endif