Fix typo in bug template (facebook#7317)

Author: mvasin

.github/ISSUE_TEMPLATE/bug_report.md

@@ -17,7 +17,7 @@ labels: "issue: bug"
  You can find webpack docs at https://webpack.js.org/.
 -->
 
-### Desribe the bug
+### Describe the bug
 
 (Write your answer here.)