fix issue #559: to json -r serializes datetime without spaces (#596)

* fix issue #559: to json -r serializes datetime without spaces

* add in a third test which checks spaces in both keys and values

* fix clippy error

crates/nu-json/src/ser.rs

@@ -4,6 +4,7 @@
 
 use std::fmt::{Display, LowerExp};
 use std::io;
+use std::io::{BufRead, BufReader};
 use std::num::FpCategory;
 
 use super::error::{Error, ErrorCode, Result};
@@ -1032,7 +1033,20 @@ where
     T: ser::Serialize,
 {
     let vec = to_vec(value)?;
-    let mut string = String::from_utf8(vec)?;
-    string.retain(|c| !c.is_whitespace());
+    let string = remove_json_whitespace(vec);
     Ok(string)
 }
+
+fn remove_json_whitespace(v: Vec<u8>) -> String {
+    let reader = BufReader::new(&v[..]);
+    let mut output = String::new();
+    for line in reader.lines() {
+        match line {
+            Ok(line) => output.push_str(line.trim().trim_end()),
+            _ => {
+                eprintln!("Error removing JSON whitespace");
+            }
+        }
+    }
+    output
+}