codecov.yml: adjust range, always post new report

Adjust codecov.io range from 50-100 to 65-100 so that 65% coverage
shows as red in reports.

Additionally, it is confusing that codecov.io updates its old post
instead of posting a new report when a branch is updated. Change
the comment behavior to "new" so Codecov deletes the old comment
and posts a new one on each run.

codecov.yml

@@ -1,6 +1,6 @@
 coverage:
  round: down
- range: "50...100"
+ range: "65...100"
  ignore:
  - "^t/.*"
  - ".*/test/.*"
@@ -24,3 +24,4 @@ coverage:
 
 comment:
  layout: "header, diff, changes, tree"
+ behavior: new