core: use cpp std14 as default

packages/hydrooj/setting.yaml

@@ -37,7 +37,7 @@ langs:
       monaco: cpp
       display: C
     cc:
-      compile: /usr/bin/g++ -Wall -std=c++11 -o ${name} foo.cc -lm
+      compile: /usr/bin/g++ -Wall -std=c++14 -o ${name} foo.cc -lm
       code_file: foo.cc
       highlight: cpp astyle-c
       monaco: cpp
@@ -46,7 +46,10 @@ langs:
       compile: /usr/bin/g++ -Wall -std=c++98 -o ${name} foo.cc -lm
       display: C++ 98
     cc.std11:
+      compile: /usr/bin/g++ -Wall -std=c++11 -o ${name} foo.cc -lm
       display: C++ 11
+    cc.std14:
+      display: C++ 14
     cc.std17:
       compile: /usr/bin/g++ -Wall -std=c++17 -o ${name} foo.cc -lm
       display: C++ 17