Fix test1.nim compilation warning.

Bump to 0.1.3

bearssl.nimble

@@ -1,6 +1,6 @@
 # Package
 
-version       = "0.1.2"
+version       = "0.1.3"
 author        = "Status Research & Development GmbH"
 description   = "BearSSL wrapper"
 license       = "MIT or Apache License 2.0"

tests/test1.nim

@@ -4,10 +4,10 @@
 # the letter 't').
 #
 # To run these tests, simply execute `nimble test`.
-
 import unittest
-
 import bearssl
 
+when defined(nimHasUsed): {.used.}
+
 test "dummy":
   check true