translation: Update chatper_backtracking / index.md (#1655)

* translation: Update chatper_backtracking / index.md

* Update index.md

Author: Phoenix0415

en/docs/chapter_backtracking/index.md

@@ -4,6 +4,6 @@
 
 !!! abstract
 
-    Like explorers in a maze, we may encounter difficulties on our path forward.
+    Like explorers in a maze, we may encounter obstacles on our path forward.
 
-    The power of backtracking allows us to start over, keep trying, and eventually find the exit to the light.
+    The power of backtracking lets us begin anew, keep trying, and eventually find the exit leading to the light.