Fix gui svg path on windows

Fix https://github.com/QGEP/qgepplugin/issues/17

Author: ponceta

src/gui/qgepplotsvgwidget.py

@@ -81,9 +81,10 @@ def __init__(self, parent, network_analyzer: QgepGraphManager, url: str=None):
 
         layout = QVBoxLayout(self)
         if url is None:
-            default_url = os.path.abspath(os.path.join(plugin_root_path(), 'svgprofile', 'index.html'))
+            # Starting with QGIS 3.4, QWebView requires paths with / even on windows.
+            default_url = plugin_root_path().replace('\\', '/') + '/svgprofile/index.html'
             url = settings.value("/QGEP/SvgProfilePath", default_url)
-            url = 'file://' + url
+            url = 'file:///' + url
 
         developer_mode = settings.value("/QGEP/DeveloperMode", False, type=bool)