Add .golangci.yml and update dep (#184)

* add .golangci.yml and update dep

Prepare environment for https://golangci.com builds by installing
libcurl-dev.
Also update dep from 0.4.1 to 0.5.0

* Fix coveralls command in TravisCI script

Dockerfile

@@ -12,7 +12,7 @@ RUN apk update && \
     libc-dev \
     git \
     pkgconfig
-ENV DEP_VERSION="0.4.1"
+ENV DEP_VERSION="0.5.0"
 RUN curl -L -s https://github.com/golang/dep/releases/download/v${DEP_VERSION}/dep-linux-amd64 -o $GOPATH/bin/dep
 RUN chmod +x $GOPATH/bin/dep
 RUN dep ensure