fix: completion installation (#53)

Author: renancaraujo

lib/src/installer/completion_installation.dart

@@ -306,7 +306,7 @@ class CompletionInstallation {
     configFile.writeAsStringSync(
       mode: FileMode.append,
       '''
-## [$scriptName] 
+\n## [$scriptName] 
 ## $description
 ${configuration!.sourceLineTemplate(scriptPath)}
 ## [/$scriptName]

test/src/installer/completion_installation_test.dart

@@ -205,7 +205,8 @@ void main() {
         expect(configFile.existsSync(), true);
 
         // ignore: leading_newlines_in_multiline_strings
-        expect(configFile.readAsStringSync(), '''## [very_good] 
+        expect(configFile.readAsStringSync(), '''
+\n## [very_good] 
 ## Completion config for "very_good"
 [[ -f ${configDir.path}/very_good.zsh ]] && . ${configDir.path}/very_good.zsh || true
 ## [/very_good]
@@ -265,7 +266,8 @@ void main() {
         installation.writeToShellConfigFile('very_good');
 
         // ignore: leading_newlines_in_multiline_strings
-        expect(rcFile.readAsStringSync(), '''## [Completion] 
+        expect(rcFile.readAsStringSync(), '''
+\n## [Completion] 
 ## Completion scripts setup. Remove the following line to uninstall
 [[ -f ${configDir.path}/zsh-config.zsh ]] && . ${configDir.path}/zsh-config.zsh || true
 ## [/Completion]
@@ -372,7 +374,8 @@ void main() {
           // rc fle includes one reference to the global config
 
           // ignore: leading_newlines_in_multiline_strings
-          expect(rcFile.readAsStringSync(), '''## [Completion] 
+          expect(rcFile.readAsStringSync(), '''
+\n## [Completion] 
 ## Completion scripts setup. Remove the following line to uninstall
 [[ -f ${configDir.path}/zsh-config.zsh ]] && . ${configDir.path}/zsh-config.zsh || true
 ## [/Completion]
@@ -385,12 +388,13 @@ void main() {
           );
 
           // ignore: leading_newlines_in_multiline_strings
-          expect(globalConfig.readAsStringSync(), '''## [very_good] 
+          expect(globalConfig.readAsStringSync(), '''
+\n## [very_good] 
 ## Completion config for "very_good"
 [[ -f ${configDir.path}/very_good.zsh ]] && . ${configDir.path}/very_good.zsh || true
 ## [/very_good]
 
-## [not_good] 
+\n## [not_good] 
 ## Completion config for "not_good"
 [[ -f ${configDir.path}/not_good.zsh ]] && . ${configDir.path}/not_good.zsh || true
 ## [/not_good]
@@ -423,7 +427,8 @@ void main() {
             ..install('not_good');
 
           // ignore: leading_newlines_in_multiline_strings
-          expect(bashProfile.readAsStringSync(), '''## [Completion] 
+          expect(bashProfile.readAsStringSync(), '''
+\n## [Completion] 
 ## Completion scripts setup. Remove the following line to uninstall
 [ -f ${configDir.path}/bash-config.bash ] && . ${configDir.path}/bash-config.bash || true
 ## [/Completion]