Add MSRV configuration to CI

Author: eldruin

.travis.yml

@@ -17,6 +17,11 @@ matrix:
       rust: nightly
       if: (branch = staging OR branch = trying) OR (type = pull_request AND branch = master)
 
+    # Minimum supported Rust version
+    - env: TARGET=x86_64-unknown-linux-gnu
+      rust: 1.35.0
+      if: (branch = staging OR branch = trying) OR (type = pull_request AND branch = master)
+
 before_install: set -e
 
 install: