DOC avoid clipping axis name in example

[seanbenhur]

Reference Issue

Solves #821

What does this implement/fix? Explain your changes.

Fixes the cropped axis name by adding plt.tight_layout() exlicitly

Any other comments?

[pep8speaks]

Hello @seanbenhur! Thanks for opening this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file examples/over-sampling/plot_shrinkage_effect.py:

Line 17:1: E402 module level import not at top of file
Line 24:1: E402 module level import not at top of file
Line 25:1: E402 module level import not at top of file
Line 38:1: E402 module level import not at top of file
Line 52:1: E402 module level import not at top of file

[glemaitre]

@seanbenhur Thanks, the rendering seems correct.