docs: catch actual exception in java doc comment (#312)

Fixes #309

Author: suraj-qlogic

google-cloud-storage/src/main/java/com/google/cloud/storage/Blob.java

@@ -726,11 +726,9 @@ public ReadChannel reader(BlobSourceOption... options) {
    * <pre>{@code
    * byte[] content = "Hello, World!".getBytes(UTF_8);
    * try (WriteChannel writer = blob.writer()) {
-   *   try {
    *     writer.write(ByteBuffer.wrap(content, 0, content.length));
-   *   } catch (Exception ex) {
-   *     // handle exception
-   *   }
+   * } catch (IOException ex) {
+   *   // handle exception
    * }
    * }</pre>
    *

google-cloud-storage/src/main/java/com/google/cloud/storage/Storage.java

@@ -2503,11 +2503,9 @@ Blob create(
    * byte[] content = "Hello, World!".getBytes(UTF_8);
    * BlobInfo blobInfo = BlobInfo.newBuilder(blobId).setContentType("text/plain").build();
    * try (WriteChannel writer = storage.writer(blobInfo)) {
-   *   try {
    *     writer.write(ByteBuffer.wrap(content, 0, content.length));
-   *   } catch (Exception ex) {
-   *     // handle exception
-   *   }
+   * } catch (IOException ex) {
+   *   // handle exception
    * }
    * }</pre>
    *