[Typo] Stoped -> Stopped

Author: Andrew Or <andrewor14@gmail.com>

Closes #847 from andrewor14/yarn-typo and squashes the following commits:

c1906af [Andrew Or] Stoped -> Stopped

(cherry picked from commit ba5d4a99425a2083fea2a9759050c5e770197e23)
Signed-off-by: Reynold Xin <rxin@apache.org>