Revert "make taskFailed non-fatal"

Originally reverted to prevent a crash when reading from an http
client raised ECONNRESET. Although this prevented a crash, laminar
stopped listening for http connections. That issue was resolved in
37bbf6ade4 (see #164), so make all exceptions fatal again.

This reverts commit 02810309fc.

src/server.cpp

@@ -172,5 +172,7 @@ kj::Promise<void> Server::handleFdRead(kj::AsyncInputStream* stream, char* buffe
 
 void Server::taskFailed(kj::Exception &&exception) {
     //kj::throwFatalException(kj::mv(exception));
-    fprintf(stderr, "taskFailed: %s\n", exception.getDescription().cStr());
+    // prettier
+    fprintf(stderr, "fatal: %s\n", exception.getDescription().cStr());
+    exit(EXIT_FAILURE);
 }