fix: wget check if file exists

tests/docs-examples-test/test_R.sh

@@ -6,7 +6,7 @@ pgrep taosd || taosd >> /dev/null 2>&1 &
 pgrep taosadapter || taosadapter >> /dev/null 2>&1 &
 
 cd ../../docs/examples/R
-wget https://repo1.maven.org/maven2/com/taosdata/jdbc/taos-jdbcdriver/3.2.4/taos-jdbcdriver-3.2.4-dist.jar
+wget -N https://repo1.maven.org/maven2/com/taosdata/jdbc/taos-jdbcdriver/3.2.4/taos-jdbcdriver-3.2.4-dist.jar
 
 jar_path=`find . -name taos-jdbcdriver-*-dist.jar`
 echo jar_path=$jar_path