[docs] [scripts] Update URL for toolchains repo

We've forked travisg's github repo into a fuchsia.googlesource.com
version that will now advance on its own.  Point at that instead.

Change-Id: I9354f42ecb438423a3fe8a04a6b5e3b5f68818bf

docs/getting_started.md

@@ -30,7 +30,7 @@ for building Magenta for ARM32, ARM64, and x86-64 architectures:
 
 ```
 cd $SRC
-git clone https://github.com/travisg/toolchains.git
+git clone https://fuchsia.googlesource.com/third_party/gcc_none_toolchains
 cd toolchains
 ./doit -a 'arm aarch64 x86_64' -f -j32
 ```

scripts/upload-toolchain.README.md

@@ -2,11 +2,11 @@
 
 These prebuilts were built automatically on the Fuchsia build infrastructure.
 
-The source used to generate these objects can be found at https://github.com/travisg/toolchains
+The source used to generate these objects can be found at https://fuchsia.googlesource.com/third_party/gcc_none_toolchains
 at the SHA that is the package filename.  The SHA will also appended to the end of this file.
 
 These tools are built by a combination of upstream sources and patches.  The patches
-can be found in the [travisg/toolchains](https://github.com/travisg/toolchains) repo and the
+can be found in the [gcc_none_toolchains](https://fuchsia.googlesource.com/third_party/gcc_none_toolchains) repo and the
 upstream sources have been mirrored to Google Storage for posterity.
 
 List all the upstream sources: