Remove support for g++-5.

.drone.yml

@@ -1,35 +1,4 @@
 pipeline:
-  gcc5:
-    image: debian:stretch-slim
-    pull: true
-    when:
-      event: [push, pull_request]
-    environment:
-      - LANG=C.utf8
-      - CXX=g++-5
-      - CXXFLAGS=-pipe -O2
-    commands:
-      - rm /etc/apt/apt.conf.d/docker-clean
-      - apt-get update -q
-      - echo "APT::Default-Release \"stretch\";" >> /etc/apt/apt.conf.d/00default_release
-      - echo "deb http://deb.debian.org/debian sid main" >> /etc/apt/sources.list.d/sid.list
-      - echo "deb http://ppa.launchpad.net/ubuntu-toolchain-r/test/ubuntu xenial main" >> /etc/apt/sources.list.d/ubuntu-toolchain-r.list
-      - apt-get install -qy gnupg
-      - gpg --keyserver hkp://keyserver.ubuntu.com --recv-keys 0x60c317803a41ba51845e371a1e9377a2ba9ef27f
-      - gpg --armor --export 0x60c317803a41ba51845e371a1e9377a2ba9ef27f | apt-key add -
-      - apt-get update -q
-      - apt-get install -qy build-essential cmake pkg-config
-      - apt-get install -qy -t xenial g++-5
-      - apt-get install -qy libcurl4-openssl-dev libjsoncpp-dev
-      - apt-get install -qy -t sid libcurlpp-dev
-      - apt-get install -qy rpm file
-      - rm -rf build && mkdir -p build && cd build
-      - cmake -DWITH_EXAMPLES=ON -DWITH_TESTS=ON ..
-      - make VERBOSE=1
-      - make install DESTDIR=install
-    volumes:
-      - /var/cache/debian-package-cache:/var/cache/apt/archives
-
   gcc6:
     image: debian:stretch-slim
     pull: true

README.md

@@ -125,7 +125,7 @@ To use the DEB package on stretch, you will need [libcurlpp0](https://packages.d
 ### Dependencies
 
 * Tested OS: Linux
-* C++ compiler (tested: gcc 5 / 6 / 7 / 8)
+* C++ compiler (tested: gcc 6 / 7 / 8)
 * [cmake](https://cmake.org/) (tested: 3.9 / 3.12)
 * [pkgconfig](https://pkgconfig.freedesktop.org/wiki/) (tested: 0.29)
 * [curlpp](http://www.curlpp.org/) (tested: 0.8)