fix FileUtilTest case

hippo4j-common/src/test/java/cn/hippo4j/common/toolkit/FileUtilTest.java

@@ -19,8 +19,6 @@ package cn.hippo4j.common.toolkit;
 
 import org.junit.Test;
 
-import java.io.UnsupportedEncodingException;
-
 public class FileUtilTest {
 
     @Test
@@ -32,8 +30,10 @@ public class FileUtilTest {
 
     @Test
     public void assertReadUtf8String2() {
-        String testText = "abcd简体繁体\uD83D\uDE04\uD83D\uDD25& *\nsecond line\n" +
-                "empty line next\n";
+        String linebreaks = System.getProperty("line.separator");
+        String testText = "abcd简体繁体\uD83D\uDE04\uD83D\uDD25& *" + linebreaks +
+                "second line" + linebreaks +
+                "empty line next" + linebreaks;
         String testFilePath = "test/test_utf8.txt";
         String contentByFileUtil = FileUtil.readUtf8String(testFilePath);
         Assert.isTrue(testText.equals(contentByFileUtil));