Change default compiler from g++ to g++ -x c++

g++ guesses the language from file extensions. -x c++ forces the
language to C++, so you don't need file extensions on your scripts.

CMakeLists.txt

@@ -1,6 +1,6 @@
 cmake_minimum_required (VERSION 3.2)
 project(compilescript
-        VERSION 0.3.4
+        VERSION 0.3.5
         LANGUAGES CXX
 )
 

compilescript.1.adoc

@@ -61,7 +61,7 @@ int main(int argc, char *argv[])
 
 [source,conf]
 ----
-compiler = "g++";
+compiler = "g++ -x c++";
 clean_after_hours = 720;
 cache_dir = "/home/user/.cache/compilescript";
 ----

src/main.cpp

@@ -42,7 +42,7 @@ using std::chrono::system_clock;
 using std::chrono::hours;
 using std::chrono::duration_cast;
 
-string compiler = "g++";
+string compiler = "g++ -x c++";
 fs::path cache_dir;
 int clean_after_hours = 30 * 24;