change version of libuv from 1_28 to 1_33

tap (train):
https://test.corp.google.com/ui#id=OCL:287864175:BASE:288298139:1578417634643:9ae99db4

all failures unrelated or flakes

PiperOrigin-RevId: 288581744

Author: Googler

cmake/external/libuv.cmake

@@ -22,7 +22,7 @@ ExternalProject_Add(
   libuv
 
   GIT_REPOSITORY https://github.com/libuv/libuv
-  GIT_TAG        v1.28.0
+  GIT_TAG        v1.33.1
   GIT_SHALLOW    1
 
   PREFIX ${PROJECT_BINARY_DIR}
@@ -31,4 +31,4 @@ ExternalProject_Add(
   BUILD_COMMAND ""
   INSTALL_COMMAND ""
   TEST_COMMAND ""
-)
+)