typo in doc

Former-commit-id: 1badd31e0e7476bb7800dcf14de0815d74f43078

include/igl/project_to_line.h

@@ -12,7 +12,7 @@
 
 namespace igl
 {
-  // PROJECT_TO_LINES  project points onto vectors, that is find the paramter
+  // PROJECT_TO_LINE  project points onto vectors, that is find the paramter
   // t for a point p such that proj_p = (y-x).*t, additionally compute the
   // squared distance from p to the line of the vector, such that 
   // |p - proj_p|² = sqr_d