Align arrows in diagrams (#39)

book/src/03_ticket_v1/09_heap.md

@@ -81,11 +81,11 @@ s.push_str("Hey");
 ```
       +---------+--------+----------+
 Stack | pointer | length | capacity |
-      |    |    |   3    |    5     |
-      +----|----+--------+----------+
-           |       
-           |       
-           v       
+      |  |      |   3    |    5     |
+      +--|  ----+--------+----------+
+         |
+         |
+         v
        +---+---+---+---+---+
 Heap:  | H | e | y | ? | ? |
        +---+---+---+---+---+

book/src/03_ticket_v1/10_references_in_memory.md

@@ -24,14 +24,14 @@ you'll get something like this in memory:
 
 ```
            --------------------------------------
-           |                                    |         
+           |                                    |
       +----v----+--------+----------+      +----|----+
 Stack | pointer | length | capacity |      | pointer |
-      |    |    |   3    |    5     |      |         |
-      +----|----+--------+----------+      +---------+
-           |        s                           r
-           |       
-           v       
+      |  |      |   3    |    5     |      |         |
+      +--|  ----+--------+----------+      +---------+
+         |          s                           r
+         |
+         v
        +---+---+---+---+---+
 Heap   | H | e | y | ? | ? |
        +---+---+---+---+---+