docs: body-case updated conventional-changelog#2919 (conventional-changelog#2950)

`condition: header is in case value` changed to `condition: body is in case value`.

Author: MadhaviMandalia

docs/reference-rules.md

@@ -94,7 +94,7 @@ Infinity
 
 #### body-case
 
-- **condition**: `header` is in case `value`
+- **condition**: `body` is in case `value`
 - **rule**: `always`
 - **value**