Numbers require at least 1 significant digit.

Address issue #96

src/core/strtod.c

@@ -291,8 +291,9 @@ int janet_scan_number(
         if (*str == '.') {
             if (seenpoint) goto error;
             seenpoint = 1;
-        }
+        } else {
             seenadigit = 1;
+        }
         str++;
     }