Revise emplace_back() to push_back() and fix Mac clang complaint.

In both cases we have a created object we want to move onto the vector.

Mac's clang objects to the first std::move() as it's applied to a
temporary and disables copy elision.

react_juce/core/EcmascriptEngine.cpp

@@ -153,7 +153,7 @@ namespace reactjuce
         {
             if (!i.isString())
                 return false;
-            sources.emplace_back(std::move(i.toString()));
+            sources.push_back(i.toString());
         }
 
         bool firstSegmentInLine = true;
@@ -182,7 +182,7 @@ namespace reactjuce
 
                 if (*p == ';')
                 {
-                    mappings.emplace_back(std::move(lineSegments));
+                    mappings.push_back(std::move(lineSegments));
                     firstSegmentInLine = true;
                 }
             }