fix problem travis' clang is have with default constructor

Former-commit-id: 3268badcbc4c7f9c55922bdea53dba76db14449e

include/igl/xml/writeDAE.cpp

@@ -25,9 +25,13 @@ IGL_INLINE bool igl::xml::writeDAE(
 
   const auto & ele = [&doc](
     const std::string tag,
-    const std::map<std::string,std::string> attribs = {},
+    // Can't just use `{}` as the default arguement because of a clang-bug 
+    // http://stackoverflow.com/questions/17264067/
+    const std::map<std::string,std::string> attribs = 
+      std::map<std::string,std::string>(),
     const std::string text="",
-    const std::list<XMLElement *> children = {}
+    const std::list<XMLElement *> children = 
+       std::list<XMLElement *>()
     )->XMLElement *
   {
     XMLElement * element = doc->NewElement(tag.c_str());