fix segmentation fault after garbage collection during process.kill [skip appveyor]
fix segmentation fault after garbage collection during process.kill [skip appveyor]

Closes #165

JCMais/node-libcurl,JCMais/node-libcurl,JCMais/node-libcurl,JCMais/node-libcurl,JCMais/node-libcurl,JCMais/node-libcurl,JCMais/node-libcurl