Update migrate_1_4.asciidoc
Update migrate_1_4.asciidoc

Added note about MVEL being removed to breaking changes.

Closes #8462

fubuki/elasticsearch,aparo/elasticsearch,aparo/elasticsearch,fubuki/elasticsearch,fubuki/elasticsearch,aparo/elasticsearch,fubuki/elasticsearch,aparo/elasticsearch,fubuki/elasticsearch,aparo/elasticsearch,aparo/elasticsearch,fubuki/elasticsearch