Bump minor version of emsdk to 1.38.47

Release Notes:

```
v1.38.47: 10/02/2019
--------------------
 - Add support for FETCH API in WASM backend. This doesn't support FETCH in the
   main thread (`USE_FETCH_WORKER=0` is enforced). rust-lang#9490
 - Redefine errno values to be consistent with wasi. This will let us avoid
   needing to convert the values back and forth as we use more wasi APIs.
   This is an ABI change, which should not be noticeable from user code
   unless you use errno defines (like EAGAIN) *and* keep around binaries
   compiled with an older version that you link against. In that case, you
   should rebuild them. See rust-lang#9545.
 - Removed build option `-s ONLY_MY_CODE` as we now have much better solutions
   for that, like building to a wasm object file or using `STANDALONE_WASM`
   etc. (see
   https://github.com/emscripten-core/emscripten/wiki/WebAssembly-Standalone).
 - Emscripten now supports the config file (.emscripten) being placed in the
   emscripten directory rather that the current user's home directory.
   See rust-lang#9543
```

src/ci/docker/scripts/emscripten.sh

@@ -19,5 +19,5 @@ exit 1
 
 git clone https://github.com/emscripten-core/emsdk.git /emsdk-portable
 cd /emsdk-portable
-hide_output ./emsdk install 1.38.46-upstream
-./emsdk activate 1.38.46-upstream
+hide_output ./emsdk install 1.38.47-upstream
+./emsdk activate 1.38.47-upstream