That is the problem right there. Avoid depending on master as it can cause problem when breaking changes are introduced.
We released a new version to support the Emscripten update released in Defold 1.2.178. You need to either update to Defold 1.2.178 (released yesterday) or depend on the previous version of the extension.
I recommend that you update Defold as the new version will result in smaller html5 builds.