docs: commit-graph: fix some whitespace in the diagram

In the merge diagram, some whitespace is missing which
makes it a bit confusing, fix that.

Signed-off-by: Johannes Berg <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: jmberg

Documentation/technical/commit-graph.txt

@@ -210,20 +210,20 @@ file.
 			    +---------------------+
 			    |                     |
  +-----------------------+  +---------------------+
- |  graph-{hash2} |->|                     |
+ |  graph-{hash2}        |->|                     |
  +-----------------------+  +---------------------+
 	  |                 |                     |
  +-----------------------+  +---------------------+
  |                       |  |                     |
- |  graph-{hash1} |->|                     |
+ |  graph-{hash1}        |->|                     |
  |                       |  |                     |
  +-----------------------+  +---------------------+
 	  |                  tmp_graphXXX
  +-----------------------+
  |                       |
  |                       |
  |                       |
- |  graph-{hash0} |
+ |  graph-{hash0}        |
  |                       |
  |                       |
  |                       |