message: Update call_graph.h
  contex -> context
diff: @@ -30,7 +30,7 @@ namespace xla {
  // The context in which a computation is called by another computation.
  enum class CallContext {
  - // In a parallel contex the computation is applied to each element of the
  + // In a parallel context the computation is applied to each element of the
  // array argument(s). kMap and kReduce instructions call computations in
  // parallel context.
  kParallel,
  