update mkdocs dependencies

to the current stable version, per pip

Also update mkdocs.yml to use new "nav" syntax.

Also python from 2.7 to 3.6

Author: isaacvetter

mkdocs.yml

@@ -1,5 +1,5 @@
 site_name: FHIRcast
-pages:
+nav:
     - Home: index.md
     - Launch Scenarios: launch-scenarios.md
     - Security Considerations: security-considerations.md

requirements.txt

@@ -1,13 +1,13 @@
 backports-abc==0.5
-certifi==2018.1.18
-click==6.7
+certifi==2018.11.29
+click==7.0
 Jinja2==2.10
-livereload==2.5.1
-Markdown==2.6.11
-MarkupSafe==1.0
-mkdocs==0.17.3
-PyYAML==3.12
+livereload==2.6.0
+Markdown==3.0.1
+MarkupSafe==1.1.0
+mkdocs==1.0.4
+PyYAML==3.13
 singledispatch==3.4.0.3
-six==1.11.0
-tornado==4.5.3
-mkdocs-material==2.7.0
+six==1.12.0
+tornado==5.1.1
+mkdocs-material==3.2.0

runtime.txt

@@ -1 +1 @@
-python-2.7.14
+python-3.6.2