Travis, please test traits with no_std

ci/test_full.sh

@@ -10,6 +10,10 @@ for package in bigint complex integer iter rational traits; do
   cargo test --manifest-path $package/Cargo.toml
 done
 
+# Only num-tratis supports no_std at the moment.
+cargo build --manifest-path traits/Cargo.toml --no-default-features
+cargo test --manifest-path traits/Cargo.toml --no-default-features
+
 # Each isolated feature should also work everywhere.
 for feature in '' bigint rational complex; do
   cargo build --verbose --no-default-features --features="$feature"