sysstr.nim: fix minor typos

lib/system/sysstr.nim

@@ -293,7 +293,7 @@ proc setLengthSeq(seq: PGenericSeq, elemSize, newLen: int): PGenericSeq {.
 
     # XXX: zeroing out the memory can still result in crashes if a wiped-out
     # cell is aliased by another pointer (ie proc parameter or a let variable).
-    # This is a tought problem, because even if we don't zeroMem here, in the
+    # This is a tough problem, because even if we don't zeroMem here, in the
     # presence of user defined destructors, the user will expect the cell to be
     # "destroyed" thus creating the same problem. We can destoy the cell in the
     # finalizer of the sequence, but this makes destruction non-deterministic.
@@ -420,7 +420,7 @@ proc nimParseBiggestFloat(s: string, number: var BiggestFloat,
     return 0
 
   if s[i] in {'0'..'9'}:
-      first_digit = (s[i].ord - '0'.ord)
+    first_digit = (s[i].ord - '0'.ord)
   # Integer part?
   while s[i] in {'0'..'9'}:
     inc(kdigits)