fix some comments (#47)

Author: dgoffredo

src/datadog/environment.h

@@ -72,7 +72,7 @@ inline const char* const variable_names[] = {
 StringView name(Variable variable);
 
 // Return the value of the specified environment `variable`, or return
-// `std::nullptr` if that variable is not set in the environment.
+// `nullopt` if that variable is not set in the environment.
 Optional<StringView> lookup(Variable variable);
 
 nlohmann::json to_json();

src/datadog/span.h

@@ -160,7 +160,7 @@ class Span {
   void inject(DictWriter& writer) const;
 
   // Return a reference to this span's trace segment.  The trace segment has
-  // member functions that effect the trace as a whole, such as
+  // member functions that affect the trace as a whole, such as
   // `TraceSegment::override_sampling_priority`.
   TraceSegment& trace_segment();
   const TraceSegment& trace_segment() const;

src/datadog/trace_sampler.h

@@ -4,7 +4,7 @@
 // traces that originate in this process will be sent to Datadog.
 //
 // `TraceSampler` is not instantiated directly, but is instead configured via
-// `TracerConfig::span_sampler`.
+// `TracerConfig::trace_sampler`.
 //
 // When a span is extracted from an outside context (i.e.
 // `Tracer::extract_span`), then the trace sampling decision is included in the