Fix capitalization

src/mainwindow.ui

@@ -525,7 +525,7 @@
           <item>
            <widget class="QLabel" name="lblMinerFeeUSD">
             <property name="text">
-             <string>       </string>
+             <string/>
             </property>
            </widget>
           </item>
@@ -914,12 +914,12 @@
   </action>
   <action name="actionCheck_for_Updates">
    <property name="text">
-    <string>Check github.com for &amp;Updates</string>
+    <string>Check github.com for &amp;updates</string>
    </property>
   </action>
   <action name="actionTurnstile_Migration">
    <property name="text">
-    <string>Sapling &amp;Turnstile</string>
+    <string>Sapling &amp;turnstile</string>
    </property>
    <property name="shortcut">
     <string>Ctrl+A, Ctrl+T</string>
@@ -927,12 +927,12 @@
   </action>
   <action name="actionImport_Private_Key">
    <property name="text">
-    <string>&amp;Import Private Key</string>
+    <string>&amp;Import private key</string>
    </property>
   </action>
   <action name="actionExport_All_Private_Keys">
    <property name="text">
-    <string>Export All Private Keys</string>
+    <string>Export all private keys</string>
    </property>
   </action>
   <action name="actionz_board_net">
@@ -945,7 +945,7 @@
   </action>
   <action name="action_Address_Book">
    <property name="text">
-    <string>Address &amp;Book</string>
+    <string>Address &amp;book</string>
    </property>
    <property name="shortcut">
     <string>Ctrl+B</string>