[rack-iodine] Reduce threads

More threads seem to cause issues.

Author: p8

frameworks/rack-iodine/Dockerfile

@@ -12,7 +12,7 @@ ENV RUBY_MN_THREADS=1
 ENV RACK_ENV=production
 # Negative values are fractions of CPU cores
 ENV WORKERS=-1
-ENV THREADS=4
+ENV THREADS=1
 
 WORKDIR /app