Replace weird Unicode quotes with ASCII ones

Author: kierdavis

docs/source/kit/servo-board.rst

@@ -38,7 +38,7 @@ servo board 12V connector when it is correctly powered.
 Case Dimensions
 ---------------
 
-The case measures 68x68x21mm. Don’t forget that the cables will stick
+The case measures 68x68x21mm. Don't forget that the cables will stick
 out.
 
 Specification