Fixing capitalization of PyPi.

README.md

@@ -53,7 +53,7 @@ People who are a little more adventurous can also try our nightly binaries:
 **Nightly pip packages**
 * We are pleased to announce that TensorFlow now offers nightly pip packages
 under the [tf-nightly](https://pypi.python.org/pypi/tf-nightly) and
-[tf-nightly-gpu](https://pypi.python.org/pypi/tf-nightly-gpu) project on pypi.
+[tf-nightly-gpu](https://pypi.python.org/pypi/tf-nightly-gpu) project on PyPi.
 Simply run `pip install tf-nightly` or `pip install tf-nightly-gpu` in a clean
 environment to install the nightly TensorFlow build. We support CPU and GPU
 packages on Linux, Mac, and Windows.