fix typos in error message and comment

c++/src/capnp/arena.h

@@ -187,7 +187,7 @@ public:
 
   virtual void reportReadLimitReached() = 0;
   // Called to report that the read limit has been reached.  See ReadLimiter, below.  This invokes
-  // the VALIDATE_INPUT() macro which may throw an exception; if it return normally, the caller
+  // the VALIDATE_INPUT() macro which may throw an exception; if it returns normally, the caller
   // will need to continue with default values.
 
   virtual kj::Own<const ClientHook> extractCap(const _::StructReader& capDescriptor) = 0;

c++/src/kj/common.c++

@@ -51,7 +51,7 @@ void inlineAssertFailure(const char* file, int line, const char* expectation,
 }
 
 void unreachable() {
-  KJ_FAIL_ASSERT("Supposendly-unreachable branch executed.");
+  KJ_FAIL_ASSERT("Supposedly-unreachable branch executed.");
 
   // Really make sure we abort.
   abort();