increase minimal version in travis

Author: AnderEnder

.travis.yml

@@ -8,7 +8,7 @@ rust:
 # rustc-demangle uses feature `rename-dependency`
 - 1.32.0
 # Oldest supported version as dependency, with no features, tests, or examples.
-- 1.13.0
+- 1.27.0
 
 sudo: false
 cache: cargo
@@ -44,4 +44,4 @@ env:
 matrix:
   exclude:
   - env: FEATURES=--features=backtrace
-    rust: 1.13.0
+    rust: 1.27.0