Fix README to indicate the right minimum version (#108)

Author: eyalkoren

log4j2-ecs-layout/README.md

@@ -1,6 +1,6 @@
 # Log4j2 ECS Layout
 
-The minimum required log4j2 version is 2.7.
+The minimum required log4j2 version is 2.6.
 
 ## Step 1: add dependency
 
@@ -128,4 +128,4 @@ This means that you can't index a document where `foo` would be a different data
 
 In that example, `foo` is a string.
 Trying to index that document results in an error because the data type of `foo` can't be object and string at the same time.
- 
+