Fix Source associations

I couldn't get this set of associations to work as is. After some googling I found out about the extra `:foreign_key` options; everything worked fine after I added the changes I made here.
If the associations work as they were and I missed something then I apologize, but I think these additions are needed.
Update project_ar_basics.md

Added solution
Add my solution to Rails exercise
Added my solution

This is for the easy challenge (google homepage) only.
Added link to my solution

With random color and opacity
Added links to my solution

HTML page embedding JS implementation for 3 challenges from Project Euler
Merge pull request #358 from donaldali/patch-33

Fix Source associations
Merge pull request #359 from tim5046/patch-13

Update project_ar_basics.md
Merge pull request #360 from ruben-socal/patch-3

Add my solution to Rails exercise
Merge pull request #361 from ratiaris/patch-1

Added my solution
Merge pull request #362 from ratiaris/patch-2

Added link to my solution
Merge pull request #363 from jason-ellis/master

Add jason ellis solution and update github account
Merge pull request #364 from ratiaris/patch-3

Added links to my solution
Update project to include Donald's Solution
Update project_rails.md

added my project solution
Update project_widgets.md

updated demo link (refactored code)
Update project_events_effects.md

add solution and demo for classic snake game project.
adding John Miller to submissions
Merge pull request #365 from donaldali/patch-34

Update project to include Donald's Solution
Merge pull request #366 from betweenparentheses/patch-4

Update project_rails.md