removed support for go<1.13 since gonum does no longer builds with this version

pa-m · pa-m · commit a21c355ec24e · 2020-07-11T11:12:47.000+02:00
diff --git a/.travis.yml b/.travis.yml
@@ -2,8 +2,7 @@
 language: go
 
 go:
-  - 1.10.x
-  - 1.11.x
+  - 1.13.x
   - tip
 
 before_install:
