Bump Bazel version to 2.1.0.

TensorFlow bumped to 2.0.0 in tensorflow/tensorflow@daec6e0. In order to sync our TensorFlow submodule, we also need to update (iree-org#834).

I ran into errors building with 2.0.0 (the same as in iree-org#174), so I went with a newer version (2.1.0) that seems to work for this repository.

Closes iree-org#755

COPYBARA_INTEGRATE_REVIEW=iree-org#755 from ScottTodd:bazelversion 981f8c7
PiperOrigin-RevId: 297206662

.bazelversion

@@ -1 +1 @@
-1.1.0
+2.1.0

WORKSPACE

@@ -46,11 +46,11 @@ py_repositories()
 # bazel toolchains rules for remote execution (https://releases.bazel.build/bazel-toolchains.html).
 http_archive(
     name = "bazel_toolchains",
-    sha256 = "ca8aa49ceb47e9bee04dd67f0bec0b010032b37ebbe67147b535237e801d9a87",
-    strip_prefix = "bazel-toolchains-1.2.2",
+    sha256 = "4d348abfaddbcee0c077fc51bb1177065c3663191588ab3d958f027cbfe1818b",
+    strip_prefix = "bazel-toolchains-2.1.0",
     urls = [
-        "https://github.com/bazelbuild/bazel-toolchains/releases/download/1.2.2/bazel-toolchains-1.2.2.tar.gz",
-        "https://mirror.bazel.build/github.com/bazelbuild/bazel-toolchains/archive/1.2.2.tar.gz",
+        "https://github.com/bazelbuild/bazel-toolchains/releases/download/2.1.0/bazel-toolchains-2.1.0.tar.gz",
+        "https://mirror.bazel.build/github.com/bazelbuild/bazel-toolchains/archive/2.1.0.tar.gz",
     ],
 )
 

docs/getting_started_on_linux.md

@@ -8,20 +8,17 @@ to the documentation.
 
 ## Pre-requisites
 
-### Install Bazel >= 1.0
+### Install Bazel
 
 *Optional if you will only be using the CMake build for runtime deps.*
 
+Check the .bazelversion file for the version you should install. You can also
+use [Bazelisk](https://github.com/bazelbuild/bazelisk) to manage Bazel versions.
+
 Follow the
 [install instructions](https://docs.bazel.build/versions/master/install-ubuntu.html)
 and verify with: `bazel --version`.
 
-If you are planning on using TensorFlow/Colab, make sure that the Bazel version
-you install is
-[supported by TensorFlow](https://www.tensorflow.org/install/source#install_bazel).
-A .bazelversion file is also provided if you want to use
-[Bazelisk](https://github.com/bazelbuild/bazelisk) to manage Bazel versions.
-
 ### Install clang
 
 ```

docs/getting_started_on_windows.md

@@ -70,11 +70,11 @@ scoop install vscode
 
 TODO: Upgrade to head python.
 
-If you are planning on using TensorFlow/Colab, make sure that the Bazel version
-you install is
-[supported by TensorFlow](https://www.tensorflow.org/install/source#install_bazel).
-A .bazelversion file is also provided if you want to use
-[Bazelisk](https://github.com/bazelbuild/bazelisk) to manage Bazel versions.
+Check the .bazelversion file for the version of Bazel you should install. You
+can also use [Bazelisk](https://github.com/bazelbuild/bazelisk) to manage Bazel
+versions.
+
+TODO: Specific steps to install a compatible version of Bazel directly
 
 ## Setup MSYS2