Update src/main/java/com/metaframe/cooma/ExtensionLoader.java

小笔误修正， from [a-zA-z0-9_] to [a-zA-Z0-9_]
Merge pull request #56 from zavakid/master

正则表达式错误： from [a-zA-z0-9_] to [a-zA-Z0-9_]