Update urandom.nim for 2.0.0

It's backwards compatible with Nim < 2.0.0

uuids/urandom.nim

@@ -12,6 +12,7 @@ when defined(windows):
 
   {.push, stdcall, dynlib: "Advapi32.dll".}
 
+  when (NimMajor, NimMinor, NimPatch) < (2, 0, 0):
     when useWinUnicode:
       proc CryptAcquireContext(
         phProv: ptr HCRYPTPROV, pszContainer: WideCString,
@@ -22,6 +23,11 @@ when defined(windows):
         phProv: ptr HCRYPTPROV, pszContainer: cstring, pszProvider: cstring,
         dwProvType: DWORD, dwFlags: DWORD
       ): WINBOOL {.importc: "CryptAcquireContextA".}
+  else:
+    proc CryptAcquireContext(
+      phProv: ptr HCRYPTPROV, pszContainer: WideCString,
+      pszProvider: WideCString, dwProvType: DWORD, dwFlags: DWORD
+    ): WINBOOL {.importc: "CryptAcquireContextW".}
 
   proc CryptGenRandom(
     hProv: HCRYPTPROV, dwLen: DWORD, pbBuffer: pointer