support drive letter.
paths contains drive letter on windows like below
    org.bouncycastle:bcpkix-jdk15on:jar:1.49:compile:C:\\Users\\taichi\\.m2\\repository\\org\\bouncycastle\\bcpkix-jdk15on\\1.49\\bcpkix-jdk15on-1.49.jar
Merge pull request #10 from taichi/drive_letter_support_on_windows

support drive letter.