Works locally

.travis.yml

@@ -1,8 +1,17 @@
 sudo: true
 language: cpp
 compiler: gcc
+
 before_install:
+  # C++17
   - sudo add-apt-repository -y ppa:ubuntu-toolchain-r/test
   - sudo apt-get update -qq
-install: sudo apt-get install -qq g++-5
-script: ./build.sh
+
+install: 
+  # C++18
+  - sudo apt-get install -qq g++-6
+
+script:
+  - qmake
+  - make
+  - ./travis_qmake_gcc_cpp17

main.cpp

@@ -1,12 +1,6 @@
-auto concept LessThanComparable<typename T> {
-    bool operator<(T, T);
-}
-
-template<typename T> requires LessThanComparable<T>
-const T& min(const T &x, const T &y) {
-    return (y < x) ? y : x;
-}
+#include <tuple>
 
-int main() {
-  if (min(42,314) != 42) { return 1; }
+int main()
+{
+  static_assert("C++17"); //C++17 has a default message
 }

travis_qmake_gcc_cpp17.pro

@@ -1,10 +1,12 @@
-TEMPLATE = app
-CONFIG += console
-CONFIG -= app_bundle qt
-SOURCES += main.cpp
+# C++17
+CONFIG += c++17
+QMAKE_CXX = g++-6
+QMAKE_LINK = g++-6
+QMAKE_CC = gcc-6
+QMAKE_CXXFLAGS += -std=c++17
+
+# High warning level
 QMAKE_CXXFLAGS += -Wall -Wextra -Weffc++ -Werror
 
-QMAKE_CXX = g++-5
-QMAKE_LINK = g++-5
-QMAKE_CC = gcc-5
-QMAKE_CXXFLAGS += -std=c++17
+# Files
+SOURCES += main.cpp