Fix compilation with gcc-5

Gcc-5 seems to have a bug in its handling of template variable.

Fixes #2267

.travis.yml

@@ -21,7 +21,7 @@ before_install:
 install:
   - if [ $TRAVIS_OS_NAME = linux ]; then
       if [ "$CXX" = "g++" ]; then
-        export CXX=g++-6;
+        export CXX=g++-5;
       fi;
     elif [ $TRAVIS_OS_NAME = osx ]; then
       brew outdated gcc || brew upgrade gcc;
@@ -35,8 +35,8 @@ addons:
     sources:
       - ubuntu-toolchain-r-test
     packages:
-      - libstdc++-6-dev
-      - g++-6
+      - libstdc++-5-dev
+      - g++-5
       - libncursesw5-dev
   coverity_scan:
     project:

src/commands.cc

@@ -1498,11 +1498,10 @@ const CommandDesc declare_option_cmd = {
 };
 
 template<bool unmap>
-static auto map_key_completer =
-    [](const Context& context, CompletionFlags flags,
+static Completions map_key_completer(const Context& context, CompletionFlags flags,
                                      CommandParameters params, size_t token_to_complete,
-       ByteCount pos_in_token) -> Completions
-    {
+                                     ByteCount pos_in_token)
+{
     if (token_to_complete == 0)
         return { 0_byte, params[0].length(),
                  complete(params[0], pos_in_token, scopes) };
@@ -1524,7 +1523,7 @@ static auto map_key_completer =
                                | gather<Vector<String>>()) };
     }
     return {};
-    };
+}
 
 const CommandDesc map_key_cmd = {
     "map",