Add warning for too strict gitbook version

lib/configuration.js

@@ -121,8 +121,8 @@ Configuration.prototype.load = function() {
         if (!semver.satisfies(pkg.version, that.options.gitbook)) {
             throw "GitBook version doesn't satisfy version required by the book: "+that.options.gitbook;
         }
-        if (that.options.gitbook == "*") {
-            that.book.log.warn.ln("you should specify a gitbook version to use in your book.json, for example: "+(_.first(pkg.version.split("."))+".x.x"));
+        if (that.options.gitbook != '*' && !semver.satisfies(that.options.gitbook, semver.inc(pkg.version, 'patch'))) {
+            that.book.log.warn.ln("gitbook version specified in your book.json might be too strict for future patches, \""+(_.first(pkg.version.split("."))+".x.x")+"\" is more adequate");
         }
 
         that.options.output = path.resolve(that.options.output || path.join(that.book.root, "_book"));

package.json

@@ -17,7 +17,7 @@
         "nunjucks-autoescape": "1.0.0",
         "nunjucks-filter": "1.0.0",
         "i18n": "0.5.0",
-        "semver": "2.2.1",
+        "semver": "5.0.1",
         "npmi": "0.1.1",
         "cheerio": "0.19.0",
         "gitbook-plugin-livereload": "0.0.1",