CI: test with libm

ci/test_full.sh

@@ -8,10 +8,19 @@ echo Testing num-traits on rustc ${TRAVIS_RUST_VERSION}
 cargo build --verbose
 cargo test --verbose
 
+# test with std and libm
+cargo build --verbose --features "libm"
+cargo test --verbose --features "libm"
+
 # test `no_std`
 cargo build --verbose --no-default-features
 cargo test --verbose --no-default-features
 
+# test `no_std` with libm
+cargo build --verbose --no-default-features --features "libm"
+cargo test --verbose --no-default-features --features "libm"
+
+
 # test `i128`
 if [[ "$TRAVIS_RUST_VERSION" =~ ^(nightly|beta|stable)$ ]]; then
     cargo build --verbose --features=i128