Change front matter trailing marker for Hugo

The documentation pulled from developer.apertis.org, which utilises HotDoc
document generation uses a `...` marker at the end of it's leading
metadata whilst Hugo (as used on the website) expects `---`. change
instances of this string.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>

content/developer/apis.md

@@ -7,7 +7,7 @@ authors:
       years: [2016]
 
 license: CC-BY-SAv4.0
-...
+---
 
 # Apertis APIs
 # Platform libraries used by applications

content/developer/app-dev.md

@@ -9,7 +9,7 @@ authors:
       years: [2016]
 
 license: CC-BY-SAv4.0
-...
+---
 
 # Application development
 

content/developer/appdev-ade.md

@@ -7,7 +7,7 @@ authors:
       years: [2017]
 
 license: CC-BY-SAv4.0
-...
+---
 
 # Apertis Development Environment
 

content/developer/appdev-agents.md

@@ -10,7 +10,7 @@ authors:
       years: [2016]
 
 license: CC-BY-SAv4.0
-...
+---
 
 # Create an agent
 

content/developer/appdev-debugging.md

 ---
 short-description: "How to debug an application"
-...
+---
 
 # Debugging app in eclipse
 

content/developer/appdev-design.md

@@ -7,7 +7,7 @@ authors:
       years: [2016]
 
 license: CC-BY-SAv4.0
-...
+---
 
 # Application design
 

content/developer/appdev-hello-world.md

@@ -9,7 +9,7 @@ authors:
       years: [2016]
 
 license: CC-BY-SAv4.0
-...
+---
 
 # Hello World
 

content/developer/apps-core.md

@@ -6,7 +6,7 @@ authors:
       years: [2015, 2016]
 
 license: CC-BY-SAv4.0
-...
+---
 
 # Core applications
 

content/developer/bundle-spec.md

@@ -7,7 +7,7 @@ authors:
       years: [2016, 2017]
 
 license: CC-BY-SAv4.0
-...
+---
 
 # Apertis Application Bundle Specification, version 1.2.0
 

content/developer/connectivity.md

@@ -6,7 +6,7 @@ authors:
       years: [2015, 2016]
 
 license: CC-BY-SAv4.0
-...
+---
 
 # Connectivity
 

content/developer/cross-build-toolchain.md

@@ -7,7 +7,7 @@ authors:
       years: [2019]
 
 license: CC-BY-SAv4.0
-...
+---
 
 # Apertis Toolchain
 

content/developer/deployment-management.md

@@ -7,7 +7,7 @@ authors:
       years: [2019]
 
 license: CC-BY-SAv4.0
-...
+---
 # Deployment management
 
 ## Design

content/developer/faq.md

@@ -7,7 +7,7 @@ authors:
       years: [2016]
 
 license: CC-BY-SAv4.0
-...
+---
 
 # FAQ
 

content/developer/framework-app.md

@@ -6,7 +6,7 @@ authors:
       years: [2015, 2016]
 
 license: CC-BY-SAv4.0
-...
+---
 
 # Application framework
 

content/developer/framework-ui.md

@@ -6,7 +6,7 @@ authors:
       years: [2015, 2016]
 
 license: CC-BY-SAv4.0
-...
+---
 
 # UI framework
 

content/developer/index.md

@@ -9,7 +9,7 @@ authors:
       years: [2016]
 
 license: CC-BY-SAv4.0
-...
+---
 
 # Apertis application developer guide
 

content/developer/infrastructure-ui.md

@@ -6,7 +6,7 @@ authors:
       years: [2015, 2016]
 
 license: CC-BY-SAv4.0
-...
+---
 
 # Infrastructure UI
 

content/developer/install.md

@@ -9,7 +9,7 @@ authors:
       years: [2016]
 
 license: CC-BY-SAv4.0
-...
+---
 
 # Installing the SDK
 

content/developer/internet.md

@@ -6,7 +6,7 @@ authors:
       years: [2015, 2016]
 
 license: CC-BY-SAv4.0
-...
+---
 
 # Internet services
 

content/developer/licensing.md

@@ -7,7 +7,7 @@ authors:
       years: [2016]
 
 license: CC-BY-SAv4.0
-...
+---
 
 # Choose a license for your application