Fix compilation error. Build on more JDKs.

Author: garydgregory

.travis.yml

@@ -18,9 +18,12 @@ sudo: false
 
 jdk:
   - openjdk7
+  - openjdk10
+  - openjdk11
+  - openjdk12
   - oraclejdk8
   - oraclejdk9
-  - openjdk10
+  - oraclejdk11
 
 script:
   - mvn

src/test/java/org/apache/commons/io/IOUtilsCopyTestCase.java

@@ -254,7 +254,7 @@ public void testCopy_readerToAppendable() throws Exception {
     public void testCopy_readerToAppendable_IO84() throws Exception {
         final long size = (long) Integer.MAX_VALUE + (long) 1;
         final Reader reader = new NullReader(size);
-        final Appendable writer = new NullWriter();
+        final NullWriter writer = new NullWriter();
 
         // Test copy() method
         assertEquals(size, IOUtils.copy(reader, writer));