Allow biopython install failure

.travis.yml

@@ -13,7 +13,7 @@ python:
 install:
     - pip wheel -f wheelhouse cython pysam numpy || true
     - pip install -f wheelhouse cython pysam pyfasta coverage pyvcf numpy || true
-    - pip install -f wheelhouse -e git+https://github.com/biopython/biopython.git#egg=biopython
+    - pip install -f wheelhouse -e git+https://github.com/biopython/biopython.git#egg=biopython || true
     - python setup.py install
     - if [ ! -f samtools-1.2 ]; then curl -sL https://github.com/samtools/samtools/releases/download/1.2/samtools-1.2.tar.bz2 | tar -xjv; fi
     - cd samtools-1.2