Disable parallel testing on CircleCI

Now that we have Dialyzer tests, we run out of memory if we run
too many at the same time.

circle.yml

@@ -17,5 +17,5 @@ dependencies:
 
 test:
   override:
-    - source $HOME/erlang/OTP-18.0.2/activate && make -j 32 -k check
-    - source $HOME/erlang/OTP-18.0.2/activate && make -j 32 -k check LEGACY=1
+    - source $HOME/erlang/OTP-18.0.2/activate && make -k check
+    - source $HOME/erlang/OTP-18.0.2/activate && make -k check LEGACY=1