typo in nightly detection

Author: RalfJung

ci/script.sh

@@ -6,7 +6,7 @@ main() {
     cross build --target $TARGET
     cross run --target $TARGET -- -V
 
-    if [ beginswith nightly $TRAVIS_RUST_VERSION ]; then
+    if beginswith nightly $TRAVIS_RUST_VERSION; then
         cargo test --features dev --target $TARGET
         cargo test --target $TARGET
     fi