build: fix the autobuilder support for emscripten.

build/run-bitten.sh

@@ -198,7 +198,7 @@ append ""
 
 append "[emscripten]"
 if em++ --version >/dev/null 2>&1; then
-    append "version = $(version | sed -ne 's/.*emcc.* \([0-9.]\{1,\}\).*/\1/p')"
+    append "version = $(em++ --version | sed -ne 's/.*emcc.* \([0-9.]\{1,\}\).*/\1/p')"
 fi
 append ""