nimble: remove nimcache setting, add release mode test task

ethash.nimble

@@ -12,16 +12,17 @@ requires "nim >= 0.18.0", "nimcrypto >= 0.1.0"
 proc test(name: string, lang: string = "c") =
   if not dirExists "build":
     mkDir "build"
-  if not dirExists "nimcache":
-    mkDir "nimcache"
   --run
-  --nimcache: "nimcache"
   switch("out", ("./build/" & name))
   setCommand lang, "tests/" & name & ".nim"
 
 task test, "Run Proof-of-Work tests (without mining)":
   test "all_tests"
 
+task testRelease, "test release mode":
+  switch("define", "release")
+  testTask()
+
 task test_mining, "Run Proof-of-Work and mining tests (test in release mode + OpenMP + march=native)":
   switch("define", "release")
   switch("define", "openmp")