Try latest-upstream again

For emscripten-core/emscripten#8045 (comment)

Author: abitrolly

.travis.yml

@@ -24,7 +24,7 @@ matrix:
     - language: rust
       #rust: "1.27.2"
       #env: EMSDK_VERSION=sdk-1.38.21-64bit
-      env: EMSDK_VERSION=latest
+      env: EMSDK_VERSION=latest-upstream
       install:
         # install emsdk
         - git clone https://github.com/emscripten-core/emsdk.git