Ensure correct DissimilarityMatrix plot dimensions
Ensure correct DissimilarityMatrix plot dimensions

Previously, a white border around the heatmap was plotted as matplotlib
does not reduce the plot area to the matrix size. This manually sets the
axis limits to ensure that no border is shown.

jairideout/scikit-bio,corburn/scikit-bio,corburn/scikit-bio,jdrudolph/scikit-bio,colinbrislawn/scikit-bio,anderspitman/scikit-bio,kdmurray91/scikit-bio,kdmurray91/scikit-bio,gregcaporaso/scikit-bio,gregcaporaso/scikit-bio,SamStudio8/scikit-bio,jairideout/scikit-bio,SamStudio8/scikit-bio,anderspitman/scikit-bio,colinbrislawn/scikit-bio,jdrudolph/scikit-bio