tighten flags; little fix

echo.sh

@@ -1,2 +1,2 @@
 #!/bin/sh
-exec dune exec --profile=release "examples/echo.exe" -- $@
+exec dune exec --display=quiet --profile=release "examples/echo.exe" -- $@

src/dune

@@ -1,8 +1,13 @@
+
+(env
+ (_
+  (flags :standard -warn-error -a+8 -w +a-4-32-40-42-44-70 -color always -safe-string
+    -strict-sequence)))
+
 (library
   (name tiny_httpd)
   (public_name tiny_httpd)
   (libraries threads seq)
-  (flags :standard -safe-string -strict-sequence -w +a-4-40-42 -warn-error -a+8)
   (wrapped false))
 
 (rule