another typo in doc

Former-commit-id: 9a51fd66e3b27be450fd895ebf5c1cafaae2bbe3

include/igl/project_to_line.h

@@ -17,7 +17,7 @@ namespace igl
   // squared distance from p to the line of the vector, such that 
   // |p - proj_p|² = sqr_d
   //
-  // [T,sqrD] = project_to_lines(P,S,D)
+  // [T,sqrD] = project_to_line(P,S,D)
   //
   // Inputs:
   //   P  #P by dim list of points to be projected