Fix documentation on enabling REPL logs

As `repl` example was moved into `deltachat_repl` crate,
the name of the log target has changed.

Author: link2xt

README.md

@@ -19,7 +19,7 @@ $ curl https://sh.rustup.rs -sSf | sh
 Compile and run Delta Chat Core command line utility, using `cargo`:
 
 ```
-$ RUST_LOG=repl=info cargo run -p deltachat-repl -- ~/deltachat-db
+$ RUST_LOG=deltachat_repl=info cargo run -p deltachat-repl -- ~/deltachat-db
 ```
 where ~/deltachat-db is the database file. Delta Chat will create it if it does not exist.
 
@@ -113,7 +113,7 @@ $ cargo build -p deltachat_ffi --release
 
 - `DCC_MIME_DEBUG`: if set outgoing and incoming message will be printed 
 
-- `RUST_LOG=repl=info,async_imap=trace,async_smtp=trace`: enable IMAP and
+- `RUST_LOG=deltachat_repl=info,async_imap=trace,async_smtp=trace`: enable IMAP and
 SMTP tracing in addition to info messages.
 
 ### Expensive tests