Note: This may be WSL specific

When any graphviz window opened by aql stays open while we terminate aql, another grapviz window pops up (containing the same graph).

Tested on

• Ubuntu 20.04 LTS in WSL Win 10.0.18363 Build 18363
• Linux K-Dev 4.4.0-18362-Microsoft #836-Microsoft Mon May 05 16:04:00 PST 2020 x86_64 x86_64 x86_64 GNU/Linux
• aql2 version: 0.0.0.r825.g572b1e23b
• dot - graphviz version 2.43.0 (0)
• X Server: VcSsrv 1.20.8.1