Allow newer version of requirements modules

Author: xinshen

app/requirements-step-1.txt

@@ -1,2 +1,2 @@
-numpy==1.14.0
-Cython==0.28.2
+numpy>=1.14.0
+Cython>=0.28.2

app/requirements-step-2.txt

@@ -1,18 +1,18 @@
-twilio==6.6.3
-ccxt==1.25.40
-structlog==17.2.0
-python-json-logger==0.1.8
-pandas==0.22.0
-stockstats==0.2.0
-TA-lib==0.4.17
-tabulate==0.8.2
-slackweb==1.0.5
-tenacity==4.8.0
-python-telegram-bot==10.0.1
-webcord==0.2
-jinja2==2.10
-requests==2.20.0
-PyYAML==3.12
-tulipy==0.2.1
-matplotlib==3.0.1
-scipy==1.1.0
+twilio>=6.6.3
+ccxt>=1.25.40
+structlog>=17.2.0
+python-json-logger>=0.1.8
+pandas>=0.22.0
+stockstats>=0.2.0
+TA-lib>=0.4.17
+tabulate>=0.8.2
+slackweb>=1.0.5
+tenacity>=4.8.0
+python-telegram-bot>=10.0.1
+webcord>=0.2
+jinja2>=2.10
+requests>=2.20.0
+PyYAML>=3.12
+tulipy>=0.2.1
+matplotlib>=3.0.1
+scipy>=1.1.0