Update .travis.yml and Dockerfile

* Updated Rubies to latest version.
* Added ruby-head as allow_failures.
  * Because it's good to know new version Ruby's issue as faster before the release.

.travis.yml

@@ -25,3 +25,9 @@ matrix:
     - env: RUBY_VERSION=ruby-2.4 OPENSSL_VERSION=libressl-2.4
     - env: RUBY_VERSION=ruby-2.4 OPENSSL_VERSION=libressl-2.5
   allow_failures:
+    - rvm: ruby-head
+      before_install:
+        - "ruby -ropenssl -e 'puts OpenSSL::OPENSSL_VERSION'"
+        - "gem update --system"
+        - "gem update bundler"
+      script: "bundle exec rake test"

tool/ruby-openssl-docker/Dockerfile

@@ -42,8 +42,8 @@ RUN curl -s https://www.openssl.org/source/openssl-1.0.2k.tar.gz | tar -C /build
       shared linux-x86_64 && \
     make && make install_sw
 
-RUN curl -s https://www.openssl.org/source/openssl-1.1.0d.tar.gz | tar -C /build/openssl -xzf - && \
-    cd /build/openssl/openssl-1.1.0d && \
+RUN curl -s https://www.openssl.org/source/openssl-1.1.0e.tar.gz | tar -C /build/openssl -xzf - && \
+    cd /build/openssl/openssl-1.1.0e && \
     ./Configure \
       --prefix=/opt/openssl/openssl-1.1.0 \
       enable-crypto-mdebug enable-crypto-mdebug-backtrace \
@@ -63,24 +63,24 @@ RUN cd /build/openssl/libressl-2.4.4 && \
       --prefix=/opt/openssl/libressl-2.4 && \
     make && make install
 
-RUN curl -s http://ftp.openbsd.org/pub/OpenBSD/LibreSSL/libressl-2.5.0.tar.gz | tar -C /build/openssl -xzf -
-RUN cd /build/openssl/libressl-2.5.0 && \
+RUN curl -s http://ftp.openbsd.org/pub/OpenBSD/LibreSSL/libressl-2.5.4.tar.gz | tar -C /build/openssl -xzf -
+RUN cd /build/openssl/libressl-2.5.4 && \
     ./configure \
       --prefix=/opt/openssl/libressl-2.5 && \
     make && make install
 
 # Supported Ruby versions: 2.3-
 RUN mkdir -p /build/ruby
-RUN curl -s https://cache.ruby-lang.org/pub/ruby/2.3/ruby-2.3.3.tar.gz | tar -C /build/ruby -xzf - && \
-    cd /build/ruby/ruby-2.3.3 && \
+RUN curl -s https://cache.ruby-lang.org/pub/ruby/2.3/ruby-2.3.4.tar.gz | tar -C /build/ruby -xzf - && \
+    cd /build/ruby/ruby-2.3.4 && \
     autoconf && ./configure \
       --without-openssl \
       --prefix=/opt/ruby/ruby-2.3 \
       --disable-install-doc && \
     make && make install
 
-RUN curl -s https://cache.ruby-lang.org/pub/ruby/2.4/ruby-2.4.0.tar.gz | tar -C /build/ruby -xzf - && \
-    cd /build/ruby/ruby-2.4.0 && \
+RUN curl -s https://cache.ruby-lang.org/pub/ruby/2.4/ruby-2.4.1.tar.gz | tar -C /build/ruby -xzf - && \
+    cd /build/ruby/ruby-2.4.1 && \
     autoconf && ./configure \
       --without-openssl \
       --prefix=/opt/ruby/ruby-2.4 \