Update URLs from `master` to `main` branch. (#2335)

docs/GetStarted/getting_started_linux_vulkan.md

diff --git a/docs/GetStarted/getting_started_linux_vulkan.md b/docs/GetStarted/getting_started_linux_vulkan.md
index 9ee8c61..5a0fd7f 100644
--- a/docs/GetStarted/getting_started_linux_vulkan.md
+++ b/docs/GetStarted/getting_started_linux_vulkan.md
@@ -39,7 +39,7 @@
 ### Quick Start
 
 The
-[dynamic_symbols_test](https://github.com/google/iree/blob/master/iree/hal/vulkan/dynamic_symbols_test.cc)
+[dynamic_symbols_test](https://github.com/google/iree/blob/main/iree/hal/vulkan/dynamic_symbols_test.cc)
 checks if the Vulkan loader and a valid ICD are accessible.
 
 Run the test:
@@ -58,7 +58,7 @@
 HAL, which includes checking for supported layers and extensions.
 
 Run the
-[device creation test](https://github.com/google/iree/blob/master/iree/hal/cts/device_creation_test.cc):
+[device creation test](https://github.com/google/iree/blob/main/iree/hal/cts/device_creation_test.cc):
 
 ```shell
 # -- CMake --
@@ -79,7 +79,7 @@
 SwiftShader's Vulkan ICD (Installable Client Driver).
 
 IREE has a
-[helper script](https://github.com/google/iree/blob/master/build_tools/third_party/swiftshader/build_vk_swiftshader.sh)
+[helper script](https://github.com/google/iree/blob/main/build_tools/third_party/swiftshader/build_vk_swiftshader.sh)
 for building SwiftShader from source using CMake:
 
 ```shell