add Japanese translation

Following original text have mistake.
Wrong: For example, for "CGCTA" and "TACCG" we found two sequences "CG"
and "TA", so the result is "CG,TA".
Correct: Wrong: For example, for "CGCTA" and "TACCG" we found three
sequences "CC", "CG" and "TA", so the result is "CC,CG,TA".
And corresponding example have same error.
Wrong: common("CGCTA", "TACCG") == "CG,TA"
Correct: common("CGCTA", "TACCG") == "CC,CG,TA"
Merge pull request #2 from sim00/master

add Japanese translation