ci: reject trailing whitespace

.travis.yml

@@ -5,6 +5,7 @@ install:
   - nix-env -iA cachix -f https://cachix.org/api/v1/install
 
 before_install:
+  - ./sh/test-whitespace
   - git lfs pull
 
 script:

sh/test-whitespace

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+
+whitespace=$(find . \
+             \( -path ./.git -o \
+                -path ./nix -o \
+                -path ./bin \) -prune \
+             -o -type f -exec egrep -lI " +$" {} \;);
+
+if [ ! -z "$whitespace" ]
+then
+  echo "found trailing whitespace in:";
+  echo "$whitespace";
+  exit 1;
+fi