Upgrading the pyyaml version (#338)

Co-authored-by: Tushar Dey <tshdy@amazon.com>

Author: TusharKanekiDey

docker/2.1.0/py2/Dockerfile.cpu

@@ -101,7 +101,7 @@ RUN ${PIP} install --no-cache-dir -U \
     keras_preprocessing==1.1.0 \
     keras==2.3.1 \
     python-dateutil==2.8.1 \
-    pyYAML==5.2 \
+    pyYAML==5.3.1 \
     requests==2.22.0 \
     awscli \
     mpi4py==3.0.3 \

docker/2.1.0/py2/Dockerfile.gpu

@@ -134,7 +134,7 @@ RUN ${PIP} install --no-cache-dir -U \
     keras_preprocessing==1.1.0 \
     keras==2.3.1 \
     python-dateutil==2.8.1 \
-    pyYAML==5.2 \
+    pyYAML==5.3.1 \
     requests==2.22.0 \
     awscli \
     mpi4py==3.0.3 \

docker/2.1.0/py3/Dockerfile.cpu

@@ -102,7 +102,7 @@ RUN ${PIP} install --no-cache-dir -U \
     keras==2.3.1 \
     smdebug==0.7.1 \
     python-dateutil==2.8.1 \
-    pyYAML==5.2 \
+    pyYAML==5.3.1 \
     requests==2.22.0 \
     awscli \
     mpi4py==3.0.3 \

docker/2.1.0/py3/Dockerfile.gpu

@@ -146,7 +146,7 @@ RUN ${PIP} install --no-cache-dir -U \
     keras==2.3.1 \
     smdebug==0.7.1 \
     python-dateutil==2.8.1 \
-    pyYAML==5.2 \
+    pyYAML==5.3.1 \
     requests==2.22.0 \
     awscli \
     mpi4py==3.0.3 \