readline: fix `concievably` typo in readline.js

Fixes: https://github.com/nodejs/node/issues/8951
PR-URL: https://github.com/nodejs/node/pull/8953
Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

lib/readline.js

@@ -369,7 +369,7 @@ Interface.prototype._normalWrite = function(b) {
 
     // got one or more newlines; process into "line" events
     var lines = string.split(lineEnding);
-    // either '' or (concievably) the unfinished portion of the next line
+    // either '' or (conceivably) the unfinished portion of the next line
     string = lines.pop();
     this._line_buffer = string;
     lines.forEach(function(line) {