Update .travis and Dockerfile

Author: wzshiming

.travis.yml

@@ -4,7 +4,7 @@ notifications:
   email: false
 jobs:
   include:
-    - go: 1.13.x
+    - go: 1.15.x
       stage: deploy
       go_import_path: github.com/wzshiming/crun
       install: skip

Dockerfile

@@ -9,4 +9,4 @@ RUN upx /go/bin/*
 
 FROM scratch
 COPY --from=upx /go/bin/ /usr/local/bin/
-ENTRYPOINT ["crun"]
+ENTRYPOINT ["/usr/local/bin/crun"]