typo in doc

Former-commit-id: a1a4024bc92e9f299b3c83e3a97c7b4f4428d915

include/igl/cumsum.h

@@ -20,7 +20,7 @@ namespace igl
   //   DerivedY  Type of matrix Y
   // Inputs:
   //   X  m by n Matrix to be cumulatively summed.
-  //   dim  dimension to take cumlative sum (1 or 2)
+  //   dim  dimension to take cumulative sum (1 or 2)
   // Output:
   //   Y  m by n Matrix containing cumulative sum.
   //