Run nghttpx integration test with cmake build

Run nghttpx integration test with cmake build.  Autotools build erases
artifacts for packaging tests, so we cannot run nghttpx integration
test with autotools build at the moment.

Relay on go modules to download dependencies.

.travis.yml

@@ -78,11 +78,11 @@ script:
     fi
   - |
     if [ "$CI_BUILD" = "cmake" ]; then
+      make
       make check
+      # Integration tests for nghttpx; autotools build erases build
+      # for packaging test.
+      cd integration-tests
+      export GO111MODULE=on
+      make it
     fi
-  # As of April, 23, 2016, golang http2 build fails, probably because
-  # the default go version is too old.
-  # - cd integration-tests
-  # - export GOPATH="$PWD/integration-tests/golang"
-  # - make itprep
-  # - make it

README.rst

@@ -323,12 +323,7 @@ its testing framework.  We depend on the following libraries:
 * golang.org/x/net/websocket
 * https://github.com/tatsuhiro-t/go-nghttp2
 
-To download the above packages, after settings ``GOPATH``, run the
-following command under ``integration-tests`` directory:
-
-.. code-block:: text
-
-    $ make itprep
+Go modules will download these dependencies automatically.
 
 To run the tests, run the following command under
 ``integration-tests`` directory:

integration-tests/Makefile.am

@@ -39,11 +39,6 @@ EXTRA_DIST = \
 	req-return.rb \
 	resp-return.rb
 
-itprep:
-	go get -d -v golang.org/x/net/http2
-	go get -d -v github.com/tatsuhiro-t/go-nghttp2
-	go get -d -v golang.org/x/net/websocket
-
 it:
 	for i in $(GO_FILES); do [ -e $(builddir)/$$i ] || cp $(srcdir)/$$i $(builddir); done
 	sh setenv go test -v