Fixed: error in topic-branches-2.svg

[iidear]

• [x] I provide my work under the project license.
• [x] I grant such license of my work as is required for the purposes of future print editions to Ben Straub and Scott Chacon.

Changes

• Chapter 3.4 Figure 29. History after merging dumbidea and iss91v2. C14 should not be ahead of C11
• topic-branches-2.png needs modification too, but I don't know how to generate the same quality png

Context