Fix for lab3 guide

Added "java" folder to the build.gradle file.
I got the the Travis error with build.gradle from old description lab3.
Travis said that I have copied the code from myself.
https://travis-ci.org/UNN-VMK-Software/agile-course-practice/builds/45060092
for example:
Copy-paste rate: 2 times
[**************** Found in: ****************]
/home/travis/build/UNN-VMK-Software/agile-course-practice/code/Ljaljushkin-Nikolay/Infrastructure/src/main/java/ru/unn/agile/ColorConverter/infrastructure/DatedTextLogger.java, started @9 line
/home/travis/build/UNN-VMK-Software/agile-course-practice/code/Ljaljushkin-Nikolay/Infrastructure/src/main/java/ru/unn/agile/ColorConverter/infrastructure/DatedTextLogger.java, started @9 line