fix: corrected ndjson key-value formatting (#25)

rust-lang/log#400
was merged upstream and caused this crate's json key-value logging to break.

This is problem for Tide, which uses key-value logging in it's default log middleware.

Fixes: #17
Refs: http-rs/tide#752

Co-authored-by: Irina Shestak <[email protected]>

Author: Fishrock123

src/ndjson.rs

@@ -56,7 +56,7 @@ fn format_kv_pairs<'b>(mut out: &mut StdoutLock<'b>, record: &Record) {
             key: kv::Key<'kvs>,
             val: kv::Value<'kvs>,
         ) -> Result<(), kv::Error> {
-            write!(self.string, ",\"{}\":{}", key, val)?;
+            write!(self.string, ",\"{}\":\"{}\"", key, val)?;
             Ok(())
         }
     }