Fix Response.InputStreamBody missing toString implementation (#1022)

Fixes #981

Author: tomdaly

core/src/main/java/feign/Response.java

@@ -32,6 +32,7 @@
 import static feign.Util.checkState;
 import static feign.Util.decodeOrDefault;
 import static feign.Util.valuesOrEmpty;
+import static feign.Util.toByteArray;
 
 /**
  * An immutable response to an http invocation which only returns string content.
@@ -277,6 +278,15 @@ public Reader asReader(Charset charset) throws IOException {
     public void close() throws IOException {
       inputStream.close();
     }
+
+    @Override
+    public String toString() {
+        try {
+            return new String(toByteArray(inputStream), UTF_8);
+        } catch (Exception e) {
+            return super.toString();
+        }
+    }
   }
 
   private static final class ByteArrayBody implements Response.Body {