doc: white space unification in repl.md

Add an infix space in an argument list.
Change `>` into `> ` in code bits and output examples.
Explicitly clarify that default REPL prompt contains a trailing space.

PR-URL: https://github.com/nodejs/node/pull/10244
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/repl.md

@@ -372,7 +372,8 @@ added: v0.1.91
 -->
 
 * `options` {Object | String}
-  * `prompt` {String} The input prompt to display. Defaults to `> `.
+  * `prompt` {String} The input prompt to display. Defaults to `> `
+    (with a trailing space).
   * `input` {Readable} The Readable stream from which REPL input will be read.
     Defaults to `process.stdin`.
   * `output` {Writable} The Writable stream to which REPL output will be