Add Flask as a dependency

Author: pglombardo

requirements.txt

@@ -3,3 +3,4 @@ fysom>=2.1.2
 opentracing>=1.2.1
 basictracer>=2.2.0
 autowrapt>=1.0
+flask>=0.12.2

setup.py

@@ -11,7 +11,7 @@
       packages=find_packages(exclude=['tests', 'examples']),
       long_description="The instana package provides Python metrics and traces for Instana.",
       zip_safe=False,
-      setup_requires=['nose>=1.0'],
+      setup_requires=['nose>=1.0', 'flask>=0.12.2'],
       install_requires=['autowrapt>=1.0',
                         'fysom>=2.1.2',
                         'opentracing>=1.2.1,<1.3',