Remove MSVC compiler warning.

Makefile

@@ -357,7 +357,7 @@ uninstall:
 #################
 
 format:
-	tools/format.sh
+	sh tools/format.sh
 
 grammar: build/janet.tmLanguage
 build/janet.tmLanguage: tools/tm_lang_gen.janet $(JANET_TARGET)

src/core/value.c

@@ -703,7 +703,7 @@ Janet janet_lengthv(Janet x) {
                 return janet_wrap_number(len);
 #else
                 if (len < (size_t) JANET_INTMAX_INT64) {
-                    return janet_wrap_number(len);
+                    return janet_wrap_number((double) len);
                 } else {
                     janet_panicf("integer length %u too large", len);
                 }

tools/format.sh

@@ -1,4 +1,4 @@
-#!/usr/bin/env bash
+#!/usr/bin/env sh
 
 # Format all code with astyle