package/ci: reduce parallelism for the ES2 build as well.

Ugh...

package/ci/circleci.yml

@@ -335,11 +335,11 @@ jobs:
     steps:
     - install-base-linux:
         extra: libsdl2-dev libglfw3-dev wget unzip
-    # In this case it gets stuck even with 24 jobs. Only on GCC, usually when
+    # In this case it gets stuck even with 20 jobs. Only on GCC, usually when
     # the huge TradeAbstractImporterTest / TradeMaterialDataTest get involved.
     # TODO: revisit when we get rid of more STL / deprecated includes
     - cap-ninja-jobs:
-        count: 20
+        count: 16
     - install-gcc-4_8
     - install-cmake:
         version: "3.4.3"