patch 8.0.0363: Travis is too slow to keep up with patches

Problem:    Travis is too slow to keep up with patches.
Solution:   Increase git depth to 20
diff --git a/.travis.yml b/.travis.yml
index 0ab1333..2315742 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -25,7 +25,7 @@
 sudo: false
 
 git:
-  depth: 10
+  depth: 20
 
 # instead of a 2*2*8 matrix (2*os + 2*compiler + 8*env),
 # exclude some builds on mac os x and linux