travis: try to fix the build on emscripten

The emsdk-portable .tar.gz now extracts to emsdk-portable instead of
emsdk_portable. Handle that.

src/ci/docker/emscripten/build-emscripten.sh

@@ -29,7 +29,20 @@ exit 1
 }
 
 curl https://s3.amazonaws.com/mozilla-games/emscripten/releases/emsdk-portable.tar.gz | \
-      tar xzf -
+    tar xzf -
+
+# Some versions of the EMSDK archive have their contents in .emsdk-portable
+# and others in emsdk_portable. Make sure the EMSDK ends up in a fixed path.
+if [ -d emsdk-portable ]; then
+    mv emsdk-portable emsdk_portable
+fi
+
+if [ ! -d emsdk_portable ]; then
+    echo "ERROR: Invalid emsdk archive. Dumping working directory." >&2
+    ls -l
+    exit 1
+fi
+
 source emsdk_portable/emsdk_env.sh
 hide_output emsdk update
 hide_output emsdk install --build=Release sdk-tag-1.37.1-32bit