Update go image to dlv 1.3.0 (#28)

Author: briandealwis

go/Dockerfile

@@ -1,7 +1,7 @@
-FROM golang:1.11 as delve
-RUN curl --location --output delve-1.2.0.tar.gz https://github.com/go-delve/delve/archive/v1.2.0.tar.gz \
- && tar xzf delve-1.2.0.tar.gz
-RUN cd delve-1.2.0/cmd/dlv && go install
+FROM golang:1.12 as delve
+RUN curl --location --output delve-1.3.0.tar.gz https://github.com/go-delve/delve/archive/v1.3.0.tar.gz \
+ && tar xzf delve-1.3.0.tar.gz
+RUN cd delve-1.3.0/cmd/dlv && go install
 
 # Now populate the duct-tape image with the language runtime debugging support files
 # The debian image is about 95MB bigger