fix conflict logical in properties namesapce. (#2066)

fix conflict logical in properties config.

apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/component/txtresolver/PropertyResolver.java

@@ -81,7 +81,7 @@ public class PropertyResolver implements ConfigTextResolver {
         keyCount++;
         String[] kv = parseKeyValueFromItem(item);
         if (kv != null) {
-          keys.add(kv[0]);
+          keys.add(kv[0].toLowerCase());
         } else {
           throw new BadRequestException("line:" + lineCounter + " key value must separate by '='");
         }

apollo-portal/src/test/java/com/ctrip/framework/apollo/portal/component/txtresolver/PropertyResolverTest.java

@@ -28,6 +28,15 @@ public class PropertyResolverTest extends AbstractUnitTest {
     }
   }
 
+  @Test
+  public void testRepeatKey() {
+    try {
+      resolver.resolve(1, "a=b\nb=c\nA=d\nB=e", Collections.emptyList());
+    } catch (Exception e) {
+      Assert.assertTrue(e instanceof BadRequestException);
+    }
+  }
+
   @Test
   public void testAddItemBeforeNoItem() {
     ItemChangeSets changeSets = resolver.resolve(1, "a=b\nb=c", Collections.emptyList());